STUDIES  IN  PHYSIOLOGY 

ANATOMY    AND    HYGIENE 


STUDIES  IN  PHYSIOLOGY 

ANATOMY  AND  HYGIENE 


BY 


JAMES  EDWARD  PEABODY,  A.M. 

INSTRUCTOR  IN  BIOLOGY  IN 
THE  MORRIS  HIGH  SCHOOL.    NEW  YORK  CITT 


ILLUSTRATED 


Nefo  gorfc 
THE   MACMILLAN   COMPANY 

LONDON:  MACMILLAN  &  CO.,  LTD. 
1912 

All  rights  reserved 


BIOLOGY 

LIBRARY 

G 


COPYRIGHT,  1903,  1907, 
BY  THE  MACMILLAN  COMPANY. 

Set  up  and  electrotyped.     Published  July,  1903.    Reprinted 
February,  July,  1905 ;  July,  1906. 

New  edition,  May,  1907;  April,  1908;   February,  August,  1909; 
January,  1910  ;  March,  December,  1911;  September,  1912. 


PKEFACE 

IN  the  preparation  of  this  book  an  attempt  has  been 
made  to  combine  the  following  features :  — 

(1)  As  the  title-page  implies,  emphasis  is  constantly  laid 
on  physiology,  and  anatomical  details  are  given  only  so  far 
as  is  necessary  to  make  intelligible  the  various  physiological 
processes.      Hygiene  is  discussed  in  a  separate  section  at 
the  end  of  the  study  of  each  system ;  for,  while  believing 
that  the  lessons  of  hygiene  are  of  primary  importance,  the 
author  is  confident  that  a  youth  will  learn  these  lessons 
best  by  getting  some  comprehension  of  the  normal  action 
of  his  various  organs. 

(2)  An  experience  of  ten  years  in  teaching  physiology  to 
high  school  pupils  has  demonstrated  that  laboratory  work 
on   the  part  of  the  pupil  is  by  far  the  most  satisfactory 
method  of  presenting  this  subject.     While  this  book  is  not 
a  laboratory  guide,  it  is  intended  to  lead  the  pupil  to  study 
the  organs  and  tissues  of  his  own  body  or  those  of  other 
animals  rather   than  to  learn  text-book  statements  about 
them.     Experiments  and  demonstrations  should,  therefore, 
precede  the  study  of  a  given  topic  in  the  text-book.     (See 
Peabody's  "Laboratory  Exercises  in  Anatomy  and  Physi- 
ology."    Henry  Holt  &  Co.,  New  York  City.)  ' 

(3)  Physiological  processes  can  never  be  understood  by 
pupils  unless  they  are  taught  at  least  some  of  the  simpler 
principles  of  chemistry.     For  this  reason  the  early  chapters 
of  the  book  are  devoted  to  a  discussion  of  the  common 
elements   and  their   compounds,  to  atmospheric   pressure, 
oxidation,  and  neutralization. 

304679 


Vl  PREFACE 

(4)  In  the  course  of  study  prescribed  in  New  York  City 
for  first-year  biology,  physiology  is  taught  in  connection 
with  botany  and  zoology.    This  has  been  found  to  be  a  most 
fortunate  arrangement,  for  the  pupil  is  easily  interested  to 
consider  physiological  processes  from  a  comparative   stand- 
point.   Because  of  the  interest  added  thereby  to  the  subject, 
there  have  been  inserted  in  the  book  several  sections  on  the 
physiology  of  some  of  our  common  animals  and  plants. 

(5)  Since  pupils  sometimes  get  an  impression  that  the 
facts  of  physiology  have  always  been  known,  the  historical 
development  of  the  subject  has  been  frequently  referred  to ; 
some  of  the  mistakes  made  by  early  physiologists  have  been 
pointed  out ;  and  the  pupil  is  led  to  appreciate  the  fact  that 
a  great  many  biological  problems  are  still  unsolved. 

(6)  Throughout  the   book,   unless   common  names   fail 
to  give   sufficient  precision,  scientific  terminology  has  been 
avoided.     Whenever  technical  terms  are  used,  their  division 
into  syllables  is  given,  and  their  Latin  and  Greek  deriva- 
tions are  noted. 

(7)  In  all  States  of  the  Union  but  two  the  statute  law 
prescribes   that  a  certain   amount   of   instruction   shall  be 
given  regarding  the   effects   of  alcohol  and  narcotics.      To 
fulfill  the  requirements  of  these  laws  twenty  pages  relating 
to  this   subject   have   been   inserted.      In  this  connection 
extensive  quotations  have  been  made  from  the  most  recent 
report  of  the  Committee  of  Fifty,  on  the  "Physiological 
Aspects  of  the  Liquor  Problem."      This  non-partisan  com- 
mittee, composed  of  men  eminent  in  science  and  education, 
has  been  working  on  this  problem  for  nearly  ten  years. 
Their  conclusions  have,  therefore,  great  weight  of  authority. 

(8)  And,  finally,  while  it  cannot  be  hoped  that  this  book 
is  entirely  free  from  errors,  I  have  used  every  means  at 
hand  to  secure  this  end,  and  I  wish  to  express  my  deep 
indebtedness  to  my  friends  for  their  suggestions  and  criti- 
cisms.    The  manuscript  was  carefully  read  by  Miss  Martha 
F.  Goddard  of  the  Department  of  Biology,  Morris  High 


PREFACE  vii 

School.  Especially  valuable  criticism  has  been  given  too 
by  Mr.  Harold  E.  Foster  of  the  English  Department  of  the 
Morris  High  School,  and  by  Dr.  F.  C.  Waite  of  the  Western 
Eeserve  Medical  School,  Cleveland,  Ohio.  I  am  also  in- 
debted for  suggestions  to  Dr.  Frank  Rollins  of  the  Depart- 
ment of  Physics,  to  Mr.  Sanford  L.  Cutler  of  the  Classical 
Department,  and  to  Mr.  J.  M.  Johnson  and  other  members 
of  the  Department  of  Biology  of  the  Morris  High  School. 
In  preparing  the  chapter  on  foods  I  have  received  much 
assistance  from  a  leading  investigator  on  foods  and  nutri- 
tion. Dr.  T.  Mitchell  Prudden  of  the  College  of  Physicians 
and  Surgeons  has  made  valuable  suggestions  for  the  sec- 
tions relating  to  bacteria,  and  Dr.  0.  S.  Strong  of  Columbia 
University  has  read  and  criticised  the  chapter  on  the  ner- 
vous system.  In  1898  the  New  York  State  Science  Teach- 
ers' Association  appointed  a  Committee  of  Five,  of  which 
the  author  is  a  member,  to  find  out  what  is  known  in  regard 
to  the  effects  of  alcohol  and  narcotics  on  the  human  body. 
To  the  other  members  of  this  committee  I  am  indebted  for 
help  in  writing  the  sections  relating  to  alcohol  and  nar- 
cotics. 

J.  B.  P. 

THE  MORRIS  HIGH  SCHOOL, 
June  15, 1903. 


CONTENTS 

CHAPTER  I 

INTRODUCTION 

PAGE 

The  Study  of  an  Engine  —  The  Study  of  the  Human  Body  — 
Anatomy  —  Physiology  —  Hygiene  —  Biology  —  The  Kela- 
tion  of  Physics  and  Chemistry  to  Physiology  ...  1 

CHAPTER  II 
LESSONS  IN  CHEMISTRY 

1.  THE  STUDY  OF  A  MATCH  :   Phosphorus  —  Oxid  of  Phosphorus 

—  Sulphur  and  Oxid   of   Sulphur  —  Water  —  Carbon  and 
Carbon  Dioxid  — Test  for  Carbon  Dioxid  —  Mineral  Sub- 
stances —  Definitions  —  Elements  —  Compounds  —  Oxida- 
tion—  Summary  .........        5 

2.  A  STUDY  OF  AIR  :    Preparation  of  Oxygen  —  Atmospheric 

Pressure  —  Collection  of  Oxygen  —  Physical  Properties  of 
Oxygen  —  Chemical  Properties  of  Oxygen  —  Preparation 
of  Nitrogen  —  A  Test  for  Acids  —  The  Composition  of  Air 

—  Properties  of  Nitrogen  —  Summary          ....       11 

3.  THE  CHEMICAL  COMPOSITION  OF  THE  HUMAN  BODY:    Water 

—  Mineral  Matters  —  Gases  —  Fats  —  Carbohydrates  — 
Nitrogenous  Substances  —  Summary   .        .        .        .        .16 

CHAPTER   III 
A  STUDY  OF  LIVING  SUBSTANCE 

1.  THE  GENERAL  STRUCTURE  OF  ANIMAL  BODIES  :   Vertebrates 

and  Invertebrates  —  Regions  of  the  Body  —  Organs  — 
Tissues 20 

2.  CELLS,  THE  UNITS  OF  LIVING   SUBSTANCE  :   The   Amoeba  — 

Structure  of  a  Cell  —  Cells  of  the  Blood  —  Cells  in  Other 
Tissues  —  Intercellular  Substance  —  Definition  of  a  Tissue  .      23 
ix 


X  CONTENTS 

PAGK 

3.  SOME    OP    THE    PROPERTIES    OF   PROTOPLASM  :    Microscopic 

Appearance  —  Chemical  Composition  —  Production  of 
Energy  —  Growth  —  Repair  —  Cell  Division  ...  28 

4.  A  STUDY   OP    BACTERIA  :    Changes  caused    by    Bacteria  — 

Microscopic  Appearance  of  Bacteria  —  Size  of  Bacteria  — 
Reproduction  of  Bacteria  —  Necessary  Conditions  for  the 
Growth  of  Bacteria 32 

5.  A  STUDY  OP  YEAST  AND  FERMENTATION:  Changes  caused  by 

Yeast  —  Distillation  —  Fermentation  —  Microscopic  Ap- 
pearance of  Yeast — Reproduction  of  Yeast  —  Spore  Forma- 
tion—  Uses  of  Yeast  —  Patent  Medicines    ....      35 
SUMMARIES  :  The  Structure  of  the  Living  Human  Body  —  The 

Functions  carried  on  by  All  Protoplasm      ....      39 


CHAPTER  IV 
A  STUDY  OF  FOODS 

Why  Foods  are  needed  in  the  Body  —  Definition  of  Food        .      41 

1.  THE   COMPOSITION  OF  FOODS:   Nutrients  —  Refuse  —  Expla- 

nation of  Food-Chart  —  Percentage  of  Nutrients  in  Foods      41 

2.  TEST    FOR  THE   NUTRIENTS  :     Test  for  Proteids  —  Test  for 

Fats  —  Test  for  Starch  —  Test  for  Grape  Sugar  —  Test  for 
Mineral  Matters  —  Test  for  Water  —  Pure  Food  Laws.  .  44 

3.  How  PLANTS  MANUFACTURE  FOOD  MATERIALS  :  Carbohydrates 

—  Organs  of  a  Plant  —  Starch  Manufacture  —  Storage  of 
Starch  and  Sugar  —  Proteid  Manufacture     ....      47 

4.  USES  OF  THE  NUTRIENTS  :  —  Uses  of  Proteids  —  Uses  of  Fats 

and  Carbohydrates  —  Comparison  of  the  Uses  of  the  Nutri- 
ents —  The  Relative  Fuel  Value  of  the  Nutrients  — Uses  of 
Mineral  Matters  and  Water 50 

5.  COOKING  OF  FOODS  :  Importance  of  Proper  Cooking  —  Meth- 

ods of  cooking  Meats  —  Reasons  for  cooking  Meats  —  Soups 

—  Boiling  Meats  —  Stewing  —  Roasting  and  Broiling  —  Rea- 
sons for  cooking  Vegetables  —  Boiling  Vegetables — Bread 
Making 52 

6.  DAILY  DIET:   Diet  required  by  Americans  —  Necessity  for  a 

Mixed  Diet 56 

7.  FOOD  ECONOMY  :  Importance  of  Food  Economy  —  Economy 

in  the  Purchase  of  Food  —  Waste  of  Food  ....      57 
SUMMARY  :  Review  of  Foods  .        .      60 


CONTENTS  xi 

CHAPTER  V 
A  STUDY  OF  STIMULANTS,  NARCOTICS,  AND  POISONS         PAGB 

1.  DEFINITION  OF  STIMULANT,  NARCOTIC,  AND  POISON:  Defini- 

tion of  a  Stimulant  —  Definition  of  a  Narcotic     ...       62 

2.  TEA  AND  COFFEE  :  Use  and  Abuse  of  Tea — Use  and  Abuse 

of  Coffee 63 

3.  TOBACCO:     Effect    of    Tobacco   on  Growth  —  Tobacco  and 

Athletics 64 

4.  ALCOHOL  :  Alcohol  as  a  Possible  Food  —  Alcohol  as  a  Stimu- 

lant, a  Narcotic,  and  a  Poison  —  Business  Argument  for  Total 
Abstinence  —  Total  Abstinence  and  Life  Insurance  —  The 
Effect  upon  Dogs  of  Moderate  Drinking  of  Alcohol  .  .  66 

CHAPTER  VI 
A  STUDY  OF  BLOOD  MANUFACTURE 

Definition  of  Digestion  —  Parts  of  the  Alimentary  Canal  —  Diges- 
tive Glands 75 

1.  THE  MOUTH  CAVITY:   Walls  of  the  Mouth  Cavity  —  Mucous 

Membrane    ..........       77 

2.  THE  TEETH  :   Arrangement  of  the  Teeth  —  Kinds  of  Teeth 

—  Dental  Formula  —  Milk  Teeth  —  Structure  of  Teeth        .      77 

3.  THE  TONGUE  :   Structure  of  the  Tongue  —  Functions  of  the 

Tongue 81 

4.  THE  SALIVARY  GLANDS  :  Position  and  Action  of  the  Salivary 

Glands  —  Microscopical  Structure  of  the  Salivary  Glands  — 
Uses  of  Saliva 82 

5.  THE  THROAT  CAVITY:   The  Uvula  — The  Air  Passages  and 

the  Epiglottis  —  Breathing  and  Swallowing  —  The  Eusta- 
chian  Tubes  —  The  Process  of  Swallowing  .  .  .84 

6.  THE  ESOPHAGUS  —  Structure  of  the  Esophagus  —  Function 

of  the  Esophagus 87 

7.  THE  STOMACH:  Position,  Shape,  Size  —  The  Mucous  Lining 

and  Gastric  Glands  —  Blood  Supply  of  the  Stomach  — 
Muscles  of  the  Stomach  —  Digestion  in  the  Stomach  — 
Digestion  of  Proteids 88 

8.  THE  SMALL  INTESTINE:  Position  and  Shape  —  Peritoneum 

— Functions  of  the  Small  Intestine  —  Adaptations  for  Ab- 
sorption —  The  Villi  92 

9.  THE  LARGE  INTESTINE  :   Position,  Form,  Size  —  Ileo-caecal 

Valve  —  Vermiform  Appendix 96 

10.  THE  PANCREAS  :  Position,  Form,  Size  —  Structure  of  the 
Pancreas  —  Functions  of  the  Pancreatic  Juice  —  Digestion 
of  Fats  97 


xii  CONTENTS 

PAGE 

11.  THE  LIVER:  Position,  Form,  Size  —  Functions  of  the  Liver 

—  Functions  of  the  Bile 98 

12.  ABSORPTION  FROM  THE  ALIMENTARY  CANAL  :   Necessity  for 

Absorption  —  The  Principles  of  Osmosis  —  Law  of  Osmosis 
— Application  of  the  Principles  of  Osmosis  to  Absorption 

—  Absorption  in  Mouth,  Throat,  and  Gullet — Absorption 
in  the  Stomach  —  Absorption  in  the  Small  Intestine  —  Ab- 
sorption in  the  Large  Intestine     „ 101 

13.  SYNOPSIS  OF  DIGESTION 105 

14.  THE    HYGIENE    OF   DIGESTION  :    Importance  of   Subject  — 

Hygienic  Habits  of  Eating  — Care  of  the  Teeth  —  Adapta- 
tion of  Foods  to  Individual  Needs  —  Prevention  of  Consti- 
pation— The  Use  of  Patent  Medicines — Effects  of  Alcoholic 
Drinks  on  the  Organs  of  Digestion 106 

15.  A  COMPARATIVE  STUDY  OF  DIGESTION  :   A  Study  of  Teeth 

—  The  Tongue  in  Other  Animals  —  The  Alimentary  Canal 
of  the  Earthworm — The  Alimentary  Canal  of  the  Frog — 
The  Alimentary  Canal  of  the  Pigeon  —  The  Alimentary 
Canal  of  the  Sheep  —  Comparison  of  the  Digestive  Organs 
Studied  .        .        .109 


CHAPTER  VII 
A  STUDY  OF  THE  BLOOD 

1.  USES  OF  THE  BLOOD  :  Nutrition  in  the  Amoeba  —  Nutrition 

in  Man  —  Uses  of  the  Blood 117 

2.  A  STUDY  OF  BEEF-BLOOD:  Preparation — Blood  Clot  —  Blood 

Serum  —  Cause  of  Coagulation  —  Blood  Fibrin  —  Defibri- 
nated  Blood  —  Difference  between  Blood  Plasma  and  Blood 
Serum  —  Composition  of  Blood  Serum  —  Change  in  Blood 
on  mixing  with  Oxygen  .  .  .  .  .  .  .118 

3.  HUMAN  BLOOD:   Application  of  the  Study  of  Beef-blood  — 

Red  Blood  Corpuscles  —  White  Corpuscles  —  Amount  of 
Blood  in  the  Body .121 

4.  THE  HYGIENE  OF  THE  BLOOD  :    Conditions  affecting  the  Red 

Corpuscles  —  Conditions  affecting  the  Serum       .        .         .    123 

5.  A  COMPARATIVE  STUDY  OF  BLOOD  :  Animals  without  Blood 

—  Color  of  the  Blood  —  Temperature  of  the  Blood  —  White 
Corpuscles  —  Red  Corpuscles 125 

6.  SUMMARY  :  Chemical  Composition  of  Blood     ....     127 


CONTENTS  xiil 

CHAPTER   VIII 
A  STUDY  OF  THE  CIRCULATION  OF  BLOOD 

PAGE 

Definition  of  the  Circulation  —  Organs  of  Circulation  .        .        .     129 

1.  THE   HEART  :    Position,   Shape,    Size  —  The   Pericardium  — 

The  Heart  a  Double  Organ  —  The  Cavities  of  the  Right  and 
Left  Hearts  — The  Valves  of  the  Right  and  Left  Hearts  — 
The  Blood  Vessels  connected  with  the  Right  Heart  —  The 
Semilunar  Valves  —  The  Blood  Vessels  connected  with 
the  Left  Heart— The  Beat  of  the  Heart  — The  Action  of 
the  Valves  of  the  Heart  —  Sounds  of  the  Heart  — The  Blood 
Supply  for  the  Heart .129 

2.  THE  BLOOD  VESSELS:   Position  of  Arteries  and  the  Pulse  — 

Structure  of  Arteries  —  Position  of  the  Veins  —  The  Struc- 
ture of  Veins — Position  of  the  Capillaries  —  Importance  of 
the  Capillaries  —  Structure  of  the  Capillaries  —  Flow  of 
Blood  in  the  Web  of  a  Frog's  Foot  —  Absence  of  Pulse  in 
Capillaries  and  Veins  .  .  .  .  .  .  .  .  137 

3.  THE  CIRCULATION  OF  THE  BLOOD  :   The  Two  So-called  Sys- 

tems of  Circulation  —  The  Pulmonary  Circulation  —  The 
Systemic  Arteries  —  The  Systemic  Veins  —  The  Portal 
System  of  Veins  —  The  Circulation  but  a  Single  System  — 
Changes  in  the  Composition  of  Blood  —  Inappropriateness 
of  the  Terms  "Arterial"  and  "Venous"  —  Regulation  of 
the  Blood  Supply  to  the  Various  Organs  ....  142 

4.  THE  LYMPHATIC   SYSTEM:    The  Lymph — Changes  in  the 

Lymph  — The  Lymphatics  — The  Lacteals  .        .        .        .148 

5.  HYGIENE  OF  THE  CIRCULATORY  SYSTEM  :   Effect  of  Heat  and 

Cold  on  the  Arteries  —  Colds  and  their  Prevention  —  Effect 
of  Exercise  on  the  Heart  —  Effect  of  Exercise  on  the  Size 
of  the  Blood  Vessels  —  Treatment  of  Cuts  and  Bruises  — 
Effect  of  Alcohol  on  Organs  of  Circulation  ....  151 

6.  A  COMPARATIVE  STUDY  OF  THIS  CIRCULATION:   Circulation 

in  the  Earthworm  —  Circulation  in  the  Fish  —  Circulation 
in  the  Frog  —  Circulation  in  the  Reptiles  —  Circulation  in 
the  Birds  and  Mammals  —  Comparison  of  the  Organs  of 
Circulation  Studied  154 


XIV  CONTENTS 

CHAPTER  IX 
A  STUDY  OF  THE  SKELETON 

PAGE 

X-Ray  Pictures  — The  Uses  of  the  Bony  Framework  of  the  Body 

—  Regions  of  the  Skeleton 159 

1.  THE  SKELETON  OP  THE  ARMS  AND  LEGS  :  Bones  of  the  Arm 

—  Bones  of  the  Leg      . 160 

2.  THE   SKELETON   OF   THE    NECK  AND  TRUNK:    The  Spinal 

Column  —  The  Structure  of  a  Vertebra  —  The  Structure  of 
Atlas  and  Axis  —  Adaptations  shown  in  the  Spinal  Column 

—  The  Ribs  and  Sternum  — The  Pectoral  Girdle  — The 
Pelvic  Girdle 162 

3.  THE  SKELETON  OF  THE  HEAD  :   The  Bones  of  the  Cranium 

—  The  Bones  of  the  Face  —  Adaptations  shown  in  the 
Structure  of  the  Skull 170 

4.  DIFFERENCES   BETWEEN   THE    SKELETON   OF  A   CHILD  AND 

THAT  OF  AN  ADULT  :   Differences  in  Composition  —  Differ- 
ences in  the  Skull  —  Differences  in  the  Spinal  Column  — 
Differences  in  the  Breastbone  —  Differences  in  the  Bones 
of  the  Arm  and  of  the  Leg  .......     172 

6.  STRUCTURE  OF  BONES:  Structure  of  a  Rib  —  Structure  of  a 
Soup  Bone  —  Advantages  of  Hollow  Bones  —  Blood  Supply 
in  Bones  —  Classification  of  the  Bones  in  the  Human 
Skeleton 174 

6.  CHEMICAL  COMPOSITION  OF  BONE  :  Effect  of  Burning  Bones 

—  Action  of  Acid  on  Bones — Nutritive  Ingredients  found 

in  Bones 177 

7.  A  STUDY  OF  JOINTS  :  Definition  of  a  Joint  —  Structure  of  a 

Leg-joint  of  Lamb  —  Classification  of  Joints        .        .        .     179 

8.  THE  HYGIENE  OF  THE  SKELETON:  Food  and  the  Skeleton 

—  Effect  of  Pressure  on  Bones 182 

9.  ACCIDENTS  TO  THE  SKELETON:   Fractures  —  Dislocations  — 

Sprains .184 

10.  A  COMPARATIVE  STUDY  OF  SKELETONS:  Skeletons  of  In- 
vertebrates and  of  Vertebrates  —  Invertebrate  Skeletons  — 
Vertebrate  Skeletons  —  Anterior  Appendages  of  Mammals 
— Peculiarities  of  the  Human  Skeleton  .  •  .  .  186 


CONTENTS  XV 

CHAPTER   X 
A  STUDY  OP  THE  MUSCLES 

PAGE 

Importance  of  Muscle  Tissue  —  Kinds  of  Muscle          .        .        .     193 

1.  THE  VOLUNTARY  MUSCLES  :   The  Biceps  Muscle  —  The  Tri- 

ceps Muscle — Arrangement  of  Muscles  in  the  Body  — 
Structure  of  Voluntary  Muscle  —  Blood  Supply  of  Muscles 
—  Nerve  Supply  to  Muscles  —  Standing  —  Walking  — 
Running 194 

2.  INVOLUNTARY  MUSCLE:  Nerve  Control — Functions  —  Struc- 

ture of  Involuntary  Muscle  —  Heart  Muscle         .         .        .     201 

3.  THE  HYGIENE  OF  MUSCLE  :  Necessary  Conditions  for  Healthy 

Muscles  —  Food—  Fresh  Air— Exercise  —  Rest.         .        .     202 

4.  A  CoaiPARATivE   STUDY  OF  LOCOMOTION  :    Amoeba  —  Para- 

mecium  —  Earthworm  —  Locomotion  in  Water  —  Locomo- 
tion in  the  Air —  Locomotion  on  Land  .  .  .  205 


CHAPTER  XI 
A  STUDY  OF  RESPIRATION 

1.  NECESSITY  FOR  RESPIRATION:  Definitions  —  Necessity  for  In- 

spiration —  Necessity  for  Expiration  —  Wastes  given  off  by 

the  Lungs , 209 

2.  THE  ORGANS  OF  RESPIRATION  :   Course  taken  by  the  Air  — 

The  Nose  Cavity  — The  Throat  and  Larynx  — The  Wind- 
pipe* and  its  Branches  —  The  Lungs  —  Blood  Supply  —  The 
Pleura  —  The  Structure  of  the  Chest  Cavity  —  Enlargement 
of  the  Chest  Cavity  —  Movements  of  the  Ribs  —  Structure 
and  Movements  of  the  Diaphragm  —  How  the  Lungs  are 
filled  with  Air  —  Inspiration  and  Expiration  .  .  .  210 

3.  CHANGES  IN  AIR  AND  BLOOD  DUE  TO  RESPIRATION:   Tem- 

perature of  Inspired  and  of  Expired  Air  —  Composition  of 
Inspired  and  of  Expired  Air  —  Changes  in  the  Blood  while 
passing  through  the  Lungs 221 

4.  HYGIENE   OF   THE   RESPIRATORY   ORGANS  :    Hygienic  Habits 

of  Breathing  —  Effect  of  Exercise  on  Respiration  —  Effect 
of  Tight  Clothing  upon  Respiration  —  Diseases  of  the 
Respiratory  Organs  —  Coughing,  Sneezing,  Choking  —  Suf- 
focation —  Necessity  of  Ventilation  —  Methods  of  Ventila- 
tion —  Proper  Methods  of  Sweeping  and  Dusting  .  .  222 


xvi  CONTENTS 

PAGE 

5.  A  COMPARATIVE  STUDY  OF  RESPIRATION  :  Respiration  in 
Single-celled  Animals  —  Respiration  in  the  Earthworm  — 
Respiration  in  Fishes  —  Respiration  in  Air-breathing  Ani- 
mals—  Comparison  of  the  Organs  of  Respiration  Studied  .  229 

CHAPTER   XII 
A  STUDY  OF  THE  SKIN  AND  THE  KIDNEYS 

Characteristics  of  the  Skin  —  Uses  of  the  Skin     ....    232 

1.  ANATOMY   AND  PHYSIOLOGY  OF  THE   SKIN  :    Layers  of  the 

Skin  —  Characteristics  of  the  Epidermis  —  Structure  of  the 
Epidermis  —  Structure  of  the  Dennis  —  Nails  —  Hair  — 
Glands  of  the  Skin  —  Sebaceous  Glands  —  Perspiratory 
Glands  —  Heat  Regulation  in  the  Body  ....  233 

2.  HYGIENE  OF  THE  SKIN:   Importance  of  Bathing  —  Kinds  of 

Baths  — Care  of  the  Hair  — Care  of  the  Nails  —  Treatment 
of  Burns  —  Clothing  —  Effect  of  Alcohol  on  the  Body  Tem- 
perature    ....  240 

3.  A  COMPARATIVE  STUDY  OF  THE  SKIN  :   The  Skin  of  Inverte- 

brates—  The  Skin  of  Amphibia  —  The  Skin  of  Fishes  and 
Reptiles  — The  Skin  of  Birds  — The  Skin  of  Mammals  .  244 

4.  A  STUDY  OF  THE  SHEEP  KIDNEY:    General  Appearance  of 

the  Kidney  —  Longitudinal  Section  of  the  Kidney       .        .     248 

5.  ANATOMY  AND  PHYSIOLOGY  OF  THE  HUMAN  KIDNEY  :  Posi- 

tion and  Appearance  —  Microscopical  Structure  —  Course 
taken  by  the  Urine  —  Importance  of  the  Kidneys  —  Blood 
Supply  of  the  Kidneys  .  .  ...  .  .  .248 

6.  A  COMPARISON  OF  EXCRETORY  ORGANS:    Secretion  and  Ex- 

cretion —  The  Kidneys  and  the  Skin  —  The  Lungs  as 
Excretory  Organs  —  The  Liver  as  an  Excretory  Organ  — 
The  Kidneys  of  Vertebrates  —  The  Kidneys  of  Invertebrates  251 

CHAPTER  XIII 
A  STUDY  OF  THE  NERVOUS  SYSTEM 

The  Body  as  a  Collection  of  Organs  —  Cooperation  of  the  Organs 

—  Functions  of  the  Nervous  System  —  Parts  of  the  Nervous 
System 253 

1.  ANATOMY  OF  THE  SPINAL  CORD:   Shape  and  Size  —  Fissures 

—  Coverings  of  the  Cord  —  Cross  Section  of  the  Cord  — 
Nerve  Cells  and  Fibers  256 


CONTENTS  xvii 

PAGE 

2.  ANATOMY  OP  THE   SPINAL  NERVES  :    Number  of  Nerves  — 

Distribution  of  Nerves  —  Origin  of  the  Nerves  —  Structure 
of  a  Spinal  Nerve  —  Structure  of  a  Spinal  Ganglion  —  Rela- 
tion of  Cells  and  Fibers 260 

3.  PHYSIOLOGY  OF  THE  SPINAL  CORD  AND  THE  SPINAL  NERVES  : 

Experiments  on  Animals  —  Functions  of  Nerve  Fibers  — 
Nerve  Impulses  —  Reflex  Action 263 

4.  THE  SYMPATHETIC  NERVOUS  SYSTEM:  Anatomy  —  Physiology    266 

5.  THE  NERVOUS  SYSTEM  OF  A  FROG  :   Reason  for  Studying  a 

Frog's  Brain  —  Forebrain  —  Midbrain  —  Hindbrain  —  The 
Spinal  and  Sympathetic  Nerve  Systems  —  Summary  — 
Frog  Physiology  —  Functions  of  the  Spinal  Cord  —  Func- 
tions of  the  Hindbrain  and  Midbrain  —  Effect  of  remov- 
ing the  Cerebral  Hemispheres  —  Function  of  the  Cerebral 
Hemispheres  —  Summary 268 

6.  ANATOMY  OF  THE  HUMAN  BRAIN  :   Protection  for  the  Brain 

—  Parts  of  the  Brain  —  Hindbrain  —  Forebrain  —  Midbrain 

—  Comparison  of  Human  and  Frog  Brains  —  Section  of 
Forebrain  —  Microscopic  Structure  of  the  Brain  —  Sensory 
and  Motor  Cells  and  Fibers  — The  Cranial  Nerves      .        .    273 

7.  PHYSIOLOGY   OF   THE   BRAIN:   Reflex  Activities  —  Conscious 

Activities  —  Localization  of  Functions  in  the  Brain  — 
Habitual  Activities  — Importance  of  Habit .  .  .  .278 

8.  HYGIENE  OF  THE  NERVOUS  SYSTEM  :    Changes  in  the  Nervous 

System  during  Life  —  Necessary  Conditions  for  a  Healthful 
Kervous  System  —  Food  and  Air  —  Varied  Activity  —  Rest 

—  Effect  of  Alcohol  on  the  Nervous  System        .        .        .283 

9.  A  COMPARATIVE   STUDY  OF  THE   NERVOUS   SYSTEM  :    Nerve 

Functions  in  Amoaba  —  The  Nervous  System  of  the  Earth- 
worm—  Nervous  Functions  in  the  Earthworm  —  The  Nerv- 
ous System  of  Invertebrates  and  of  Vertebrates  —  A 
Comparison  of  Vertebrate  Brains 287 


CHAPTER   XIV 
A  STUDY  OF  THE  SENSES 

1.  THE  SENSE  OF  TOUCH:   The  Sense  Organs  of  Touch  —  Sen- 

sations of  Touch 291 

2.  GENERAL   SENSES:    Sensations  of  Temperature  —  Sensations 

of  Pain  —  Sensations  of  Hunger  and  Thirst         .        .        .     293 


XVlii  CONTENTS 

PAGE 

3.  THE  SENSE  OF  TASTE  :   Papillae  of  the  Tongue  -—  The  Taste 

Buds* —  Sensations  of  Taste 294 

4.  THE  SENSE   or  SMELL  :    The  Nasal  Cavities  —  The  Sense 

Organs  of  Smell  —  Sensations  of  Smell         .        .        .        .296 

5.  THE  SENSE  OF  SIGHT  :   Protection  for  the  Eye  —  The  Tear 

Glands  and  Ducts  —  Sebaceous  Glands  —  Movements  of 
the  Eyes  —  General  Form  of  the  Eye  —  Coats  of  the  Eye  — 
The  Lens  of  the  Eye  — The  Humors  of  the  Eye  — The  Eye 
as  a  Camera  —  Accommodation  of  the  Eye  —  Sensations  of 
Sight  — The  Blind  Spot  and  the  Yellow  Spot  —  Defective 
Eyes  —  Hygiene  of  the  Eyes 298 

6.  THE  SENSE  OF  HEARING:    The  External  Ear  — The  Middle 

Ear  —  The  Bones  of  the  Middle  Ear  —  General  Structure  of 
the  Inner  Ear  —  The  Structure  and  Functions  of  the  Semi- 
circular Canals  —  The  Structure  and  Functions  of  the 
Cochlea  —  Sensations  of  Sound  —  Loudness,  Pitch,  and 
Quality 308 


CHAPTER  XV 
A  STUDY  OF  THE  VOICE  AND  OF  SPEECH 

The  Vocal  Organs  of  Man  — The  Cartilages  of  the  Larynx  — The 
Vocal  Cords  —  Resonating  Cavities  —  Speech  —  Loudness, 
Pitch,  and  Quality  —  The  Care  of  the  Voice  —  Sounds  pro- 
duced by  Other  Animals  .  .  .  .  .  .315 


INDIX  •    321 


STUDIES   IN  PHYSIOLOGY 

ANATOMY   AND   HYGIENE 


STUDIES   IN   PHYSIOLOGY 

ANATOMY  AND   HYGIENE 
CHAPTER  I 

INTRODUCTION 

The  Study  of  an  Engine.  —  If  we  wished  to  make  a  careful 
and  scientific  study  of  a  railroad  locomotive,  it  would,  per- 
haps, be  best  for  us  first  to  go  to  a  machine  shop  where 
engines  are  built  and  repaired.  There  we  could  see  the 
construction  of  each  separate  part  and  could  also  find  how 
these  various  parts  are  put  together  to  form  a  completed 
engine. 

But  if  we  had  never  before  seen  an  engine,  the  whole 
machine  would  probably  have  little  meaning  or  interest  for 
us  until  we  had  watched  it  in  action.  We  should  then 
learn  how  the  locomotive  is  supplied  with  water  and  coal. 
We  should  see  that  the  burning  coal  converts  the  water 
into  steam,  and  that  energy  or  power  is  thus  furnished  by 
which  the  pistons  cause  the  drive  wheels  to  revolve.  All 
the  pipes,  cranks,  levers,  and  rods  we  should  find  to  be 
specially  adapted  for  starting  the  locomotive,  for  keeping  it 
in  motion,  or  for  stopping  it. 

To  understand  thoroughly,  however,  the  action  of  this 
complicated  mechanism  we  should  need  to  go  still  farther 
in  our  study.  Considerable  knowledge  of  the  principles  of 
levers  would  be  required.  We  should  have  to  investigate 
the  processes  involved  in  the  burning  of  coal  and  in  the 
change  of  water  into  steam,  and  we  should  seek  an  expla- 

B  1 


2  STUD JE^  IN  PHYSIOLOGY 

nation  of  the  force  exerted  by  the  steam.  In  other  words, 
the  scientific  student  of  an  engine  would  necessarily  study 
physics  and  chemistry,  the  sciences  that  lead  to  the  solution 
of  the  problems  just  suggested. 

And  finally,  if  we  wished  to  become  competent  engineers, 
we  should  seek  to  acquire  also  the  practical  knowledge  of 
how  to  get  the  most  work  out  of  a  locomotive.  We  should 
study  the  best  methods  of  feeding  in  the  coal  and  of 
regulating  the  supply  of  water  and  of  air;  we  should 
determine  the  amount  of  oil  required,  and  the  length  of 
time  the  engine  would  run  before  needing  a  rest. 

Let  us  now  summarize  what  we  have  learned  thus  far. 
An  engine  may  be  considered  in  at  least  three  different 
ways.  We  may  look  at  it  as  a  collection  of  various  pieces 
of  iron  and  brass,  and  may  devote  our  time  to  studying  the 
form  of  the  parts  and  the  way  they  are  put  together.  By 
watching  the  change  of  water  into  steam,  and  again  by  ob- 
serving the  movement  of  wheels  and  levers,  we  may  learn  the 
uses  of  the  parts.  Or  finally,  we  may  study  the  machine 
with  a  view  of  determining  the  most  successful  methods  of 
keeping  it  in  good  running  order. 

The  Study  of  the  Human  Body.  —  The  human  body,  too,  is 
a  machine.  But  it  is  far  more  complicated  than  any  loco- 
motive and  capable  of  doing  many  more  kinds  of  work. 
The  body  not  only  can  move  about  and  carry  things  from 
place  to  place,  but  it  can  also  grow  and  repair  itself,  and 
within  the  body  the  mind  can  feel  and  think.  Like  the 
engine,  however,  it  can  be  studied  in  three  different  ways. 
We  may  discuss  its  structure,  its  activities,  and  its  proper 
care.  When  we  are  considering  animal  machines,  these 
three  branches  of  study  are  known  respectively  as  a-nat'o-my, 
phys-i-ol'o-gy,  and  Jiy'gi-ene. 

Anatomy.  —  By  the  anatomy  of  an  animal  is  meant  the 
study  of  its  structure.  If  one  is  considering  the  anatomy  of 
the  human  body,  for  instance,  one  may  discuss  the  form  of 
the  several  parts,  their  microscopic  structure,  their  positions 


INTRODUCTION  3 

in  the  body,  and  the  connections  of  these  parts  with  each 
other.  The  anatomy  of  a  lifeless  body  can  be  studied  far 
more  completely  than  can  the  anatomy  of  a  living  animal, 
for  any  complete  knowledge  of  structure  involves  dissecting 
or  cutting  into  the  various  regions.  The  term  anatomy  is 
derived  from  two  Greek  words  which  mean  to  cut  up,  (ana '  = 
up  +  tem'nein  =  to  cut). 

Physiology.  —  For  the  study  of  physiology,  however,  a  liv- 
ing organism  is  necessary,  since  this  science  is  the  study  of 
the  uses  or  functions  of  the  various  organs.  The  functions 
of  a  cat's  claws  can  be  determined  only  by  watching  the  use 
the  cat  makes  of  them.  Man  has  found  out  the  use  of  the 
internal  organs  of  animals  largely  by  experimenting  upon 
them,  and  many  of  the  wonderful  discoveries  in  medicine 
have  been  made  by  studying  the  physiology  of  dogs,  guinea 
pigs,  and  other  animals. 

Physiology  has  for  most  of  us  a  meaning  altogether  too 
limited,  for  we  usually  confine  the  term  to  the  study  of  the 
human  body.  We  should  remember  that  it  includes  the  con- 
sideration of  the  functions  not  only  of  all  the  countless 
species  of  animals,  but  of  all  forms  of  plant  life  as  well.  And 
if  we  could  carry  our  studies  far  enough,  we  should  see  that 
similar  vital  processes  are  performed  in  the  lowest  of  plants 
and  in  the  highest  of  animals,  however  much  these  organisms 
may  differ  in  structure. 

Hygiene.  —  The  word  hygiene  is  derived  from  the  Greek 
word  hy-ge'ia,  which  means  health.  This  branch  of  science 
treats  of  the  conditions  that  tend  to  develop  and  maintain 
a  healthy  body.  It  cannot  be  studied  to  good  advantage 
until  one  becomes  acquainted  with  the  structure  and  uses  of 
the  various  parts  of  one's  body ;  it  must,  therefore,  be  pre- 
ceded by  some  knowledge  of  anatomy  and  physiology. 

Biology  (Greek  bi'os  =  life  +  log'os  =  science)  is  the  gen- 
eral name  given  to  the  study  of  all  living  things.  Hence 
this  science  treats  of  both  animals  and  plants,  and  includes 
a  consideration  of  their  anatomy,  physiology,  and  hygiene. 


4  STUDIES  IN  PHYSIOLOGY 

The  term  biology  is  usually  employed,  however,  when  we 
are  comparing  the  processes  carried  on  in  both  of  these  two 
great  kingdoms  of  animate  bodies.  If  we  confine  our  study 
to  the  structure  and  activities  of  plants  alone,  we  call  this 
part  of  the  science  botany.  Zoology,  on  the  other  hand,  treats 
of  the  anatomy  and  physiology  of  animals.  Human  physi- 
ology discusses  man,  the  highest  type  of  the  animal  king- 
dom ;  hence  it  is  a  branch  of  the  science  of  zoology,  which 
in  turn  is  one  of  the  subdivisions  of  the  study  of  biology. 

The  Relation  of  Chemistry  and  Physics  to  Physiology We 

saw  in  a  previous  section  that  a  complete  explanation  of  the 
action  of  a  locomotive  requires  some  knowledge  of  physics 
and  chemistry.  This  is  far  more  true  in  animal  physiology. 
We  may  study  the  various  parts  of  the  human  body,  and  we 
may  watch  the  activities  of  these  parts,  but  we  cannot  begin 
to  understand  the  processes  that  we  see  until  we  know  some- 
thing of  the  chemical  composition  of  lifeless  as  well  as  of 
living  things,  and  something  of  the  chemical  changes  that 
are  constantly  taking  place  all  about  us  as  well  as  within 
us.  Our  next  chapter  will  therefore  be  devoted  to  a  con- 
sideration of  some  simple  experiments  in  chemistry. 


CHAPTER  II 

LESSONS  IN  CHEMISTRY 
1.     THE  STUDY  OF  A  MATCH1 

A  SPLINTER  of  soft  pine  wood  tipped  with  a  mixture  of 
phosphorus,  sulphur,  and  other  ingredients  is  one  of  the 
commonest  necessities  of  every-day  life.  We  light  these 
matches  a  dozen  times  a  day  and  throw  them  away  half- 
burned,  never  thinking  that  we  might  learn  from  this  ap- 
parently simple  process  many  of  the  fundamental  principles 
of  chemical  science. 

Phosphorus.  —  If  in  a  dark  room  I  draw  the  tip  of  a 
match  across  my  finger,  there  is  left  behind  a  luminous 
streak.  This  is  caused  by  the  slow  burning  of  phos'pho-rus. 
To  understand  what  has  taken  place  we  must  experiment 
with  phosphorus  alone.  In  its  pure  state  it  is  a  yellowish 
white,  waxy  solid.  It  is  usually  manufactured  in  sticks 
about  the  size  of  one's  finger,  and  these,  because  of  the  great 
inflammability  of  phosphorus,  are  always  kept  under  water. 

Suppose  we  cut  off  a  bit  of  phosphorus  about  the  size  of 
a  pea,  and  hold  it  on  the  knife  tip.2  As  it  becomes  dry  it 
gives  off  little  streams  of  white  smoke,  and  the  piece  grad- 
ually diminishes  in  size.  If  it  is  rubbed  vigorously  against 
a  rough  surface,  the  waxy  mass  bursts  into  a  bright  yellow 
flame  and  soon  disappears. 

Oxid  of  Phosphorus.  —  Let  us  now  inquire  somewhat 
closely  into  this  process  of  burning.  Our  earth  is  sur- 
rounded by  a  mixture  of  gases  that  form  the  atmosphere. 

1  See  Peabody's  "Laboratory  Exercises,"  No.  1.     Holt  &  Co. 

2  Phosphorus  should  never  be  handled  with  the  fingers. 

5 


6  STUDIES   IN  PHYSIOLOGY 

Close  to  the  earth  this  air  is  comparatively  dense.  But  if 
one  could  rise  in  a  balloon  from  the  surface,  one  would  find 
that  the  air  becomes  more  and  more  rare,  and  that  it  almost 
ceases  to  exist  at  a  height  of  thirty  to  sixty  miles.  One  of 
the  constituents  of  the  atmosphere  is  a  gas  called  ox'y-gen. 
When  we  take  the  phosphorus  from  the  water,  we  expose  it 
to  this  omnipresent  oxygen  of  the  air.  This  is  all  that  is 
necessary,  for  the  mutual  attraction  between  phosphorus 
and  oxygen  is  so  great  that  the  two  straightway  combine  to 
form  a  new  substance. 

We  saw  the  white  fumes  rising  from  the  phosphorus  and 
noticed  that  some  of  the  latter  disappeared.  If  we  measured 
the  exact  amount  of  oxygen  in  the  air  before  and  after  the 
experiment,  we  should  find  that  small  quantities  of  this 
gas  also  had  disappeared.  The  white  fumes  are  therefore 
formed  by  a  chemical  union  of  phosphorus  with  oxygen, 
and  since  the  fumes  are  composed  of  these  two  substances 
alone,  the  new  compound  is  called  an  oxid  of  phosphorus. 

Every  time  we  draw  a  match  across  our  fingers,  we  cause 
a  little  of  the  phosphorus  to  combine  with  surrounding  oxy- 
gen, and  we  notice  the  peculiar  smell  of  oxid  of  phosphorus. 
When  we  scratch  the  match  more  forcibly  against  a  rough 
surface,  we  hasten  this  process  by  causing  the  heated 
phosphorus  to  combine  rapidly  with  the  oxygen  gas  of 
the  air,  and  thus  a  flame  is  produced.  In  this  chemical 
union  both  phosphorus  and  oxygen  seem  to  disappear. 
They  are  not  lost,  however ;  for  on  decomposing  or  analyz- 
ing the  white  fumes  we  find  all  of  the  phosphorus  we  had  at 
first  and  all  of  the  oxygen  taken  from  the  air. 

Sulphur  and  Oxid  of  Sulphur.  —  Let  us  light  another  match 
and  continue  our  study.  Soon  after  the  white  fumes  of 
oxid  of  phosphorus  begin  to  appear,  we  notice  the  suffocating 
odor  of  burning  sulphur.  The  sulphur  of  commerce  is 
usually  obtained  from  mines  near  active  or  extinct  vol- 
canoes and  comes  to  us  in  the  form  of  a  yellow  powder  or 
of  solid  brimstone.  If  we  treat  a  bit  of  it  as  we  did  the 


LESSONS   IN   CHEMISTRY  7 

phosphorus,  we  are  unable  to  make  it  burn,  however  vigor- 
ously we  may  rub  it  against  a  rough  surface.  When,  how- 
ever, we  touch  a  heated  nail  to  the  sulphur,  the  latter 
catches  fire  and  burns  with  a  pale  blue  flame,  giving  off  the 
same  suffocating  smell  that  we  perceived  when  the  match 
head  was  aflame. 

In  the  burning  of  sulphur  a  process  is  going  on  similar  to 
that  already  described  in  the  case  of  phosphorus.  The 
heated  sulphur  combines  with  a  certain  amount  of  the  oxy- 
gen of  the  air,  and  an  invisible  gas  is  made  which  we 
recognize  by  its  pungent  odor.  This  new  substance,  being 
composed  of  sulphur  and  oxygen,  is  called  oxid  of  sulphur. 
Our  experiment  teaches  us  that  sulphur  does  not  combine 
with  oxygen  as  readily  as  does  phosphorus,  for  the  former 
could  not  be  lighted  by  friction.  The  heat  caused  by  the 
burning  phosphorus  on  the  match  tip  is  sufficient,  however, 
to  set  fire  to  the  sulphur. 

Water.  —  We  are  now  ready  to  study  the  composition  of 
wood  itself,  and  to  note  the  changes  that  take  place  when  it 
is  burned.  If  we  hold  a  lighted  match  stick  just  beneath 
the  mouth  of  a  dry  tumbler,  we  soon  notice  that  the  inside 
of  the  glass  is  covered  with  a  film  of  moisture.  Water, 
then,  is  the  first  substance  produced  in  the  process  of  burn- 
ing wood.1  It  goes  into  the  air  in  the  form  of  vapor  and  is 
then  condensed  by  the  cool  surface  of  the  glass. 

Carbon  and  Carbon  Dioxid.  —  On  extinguishing  the  flame  of 
a  burning  match,  we  find  that  the  wood  has  been  converted 
into  a  black,  brittle  substance;  this  we  call  carbon.  As  was 
the  case  with  sulphur,  it  is  impossible  to  make  the  carbon 
burn  by  the  heat  of  friction.  If,  however,  we  put  the 
charred  wood  into  a  hot  flame,  the  carbon  catches  fire, 
gradually  disappears,  and  nothing  remains  but  a  powdery, 
gray  ash.  The  same  result  is  obtained  if  we  allow  a  match 
to  burn  as  long  as  it  will,  since  the  carbon  is  then  heated 
red  hot  by  the  burning  phosphorus  and  sulphur.  In  this 
1  We  shall  prove  later  that  water  is  an  oxid  of  a  gas  called  hydrogen. 


8  STUDIES  IN  PHYSIOLOGY 

process  the  carbon  takes  to  itself  some  of  the  oxygen  about 
it  and  forms  a  colorless,  tasteless,  odorless  gas  which  we 
may  call  oxid  of  carbon.  The  more  common  names  applied 
to  it  are  carbonic  acid  gas  and  carbon  dioxid,  the  latter  being 
the  preferable  term. 

Test  for  Carbon  Dioxid.  —  In  spite  of  the  fact  that  carbon 
dioxid  has  no  color,  taste,  or  odor,  we  can  easily  demonstrate 
its  presence  in  the  following  way.  If  we  put  some  clear 
limewater1  into  a  bottle  in  which  carbon  dioxid  has  been 
formed  by  burning  wood,  we  find  after  shaking  that  the 
liquid  loses  its  transparency  and  becomes  milky.  This 
change  in  limewater  is  always  caused  by  carbon  dioxid 
and  by  nothing  else. 

Mineral  Substances.  —  In  our  experiments  thus  far  we 
have  watched  the  formation  of  water  (oxid  of  hydrogen) 
and  the  oxids  of  phosphorus,  sulphur,  and  carbon.  Our 
match  is  at  last  reduced  to  ashes.  These  we  know  will  not 
burn.  We  may  heat  them  to  a  red  or  even  white  heat,  but 
in  most  cases  they  remain  wholly  unchanged,  and  on  cooling 
resume  their  gray  or  white  appearance.  The  ashes  of  the 
wood  are  the  mineral  matters  that  were  obtained  from  the 
earth  by  the  living  plant. 

Definitions.  —  If  we  keep  in  mind  the  experiments  we  have 
described,  certain  important  definitions  will  now  become 
clear  to  us.  All  the  materials  of  which  the  universe  is 
composed  may  be  divided  into  two  classes,  namely,  chemical 
elements  and  chemical  compounds. 

Elements.  —  Of  the  materials  of  the  universe  there  are 
certain  substances  which  chemists  are  unable  to  make  any 
simpler  in  their  composition.  Hence  they  are  called  chemi- 
cal elements.  Over  seventy  of  these  elements  are  known, 
some  of  the  most  common  being  the  carbon,  oxygen,  and 
sulphur  that  we  have  been  studying.  The  names  of  these 

1  Limewater  is  made  by  dissolving  ordinary  quicklime  in  water. 
The  solution,  after  it  is  strained  or  filtered  through  porous  paper,  is  as 
clear  as  ordinary  water. 


LESSONS  IN  CHEMISTKY  9 

elements  are  constantly  used  in  science,  and  it  has  been 
found  convenient  to  refer  to  these  substances  by  symbols, 
the  first  letter  or  letters  of  the  name  being  used  in  most 
cases.  Thus  we  mean  carbon  when  we  use  the  capital 
letter  C;  0  stands  for  oxygen;  S  for  sulphur;  and  P  for 
phosphorus.  I  stands  for  iodine,  and  so  Ee  (Latin  ferrum  = 
iron)  is  used  for  iron.  An  element  may  be  defined  as  a  sub- 
stance that  cannot  be  decomposed  into  simpler  substances. 

Compounds.  —  We  have  seen  that  a  certain  amount  of  heat 
causes  the  element  phosphorus  to  unite  with  some  of  the 
element  oxygen,  and  that  thus  a  new  substance  is  formed 
called  oxid  of  phosphorus ;  more  heat  will  produce  oxid  of 
sulphur  by  a  chemical  union  between  sulphur  and  oxygen, 
while  at  a  still  higher  temperature  carbon  unites  with 
oxygen,  forming  oxid  of  carbon  or  carbon  dioxid.  All  of 
these  oxids  are  chemical  compounds.  Hence  a  chemical  com- 
pound may  be  defined  as  a  substance  that  can  be  decomposed 
into  simpler  substances.  A  compound,  therefore,  is  formed  by 
the  chemical  union  of  two  or  more  elements. 

We  will  now  consider  the  composition  of  two  of  the  most 
important  of  the  compounds  that  we  have  been  studying. 
Eepeated  experiments  have  proved  that  one  part  of  carbon 
combines  with  two  parts  of  oxygen.  Chemists,  therefore, 
give  to  the  gas  thus  formed  the  name  carbon  dioxid  and 
represent  its  composition  in  the  symbol  C02 ;  both  name  and 
symbol  tell  us  that  it  is  composed  of  one  part  carbon  and 
two  parts  oxygen.  Water,  too,  is  a  compound,  a  fact  that 
can  be  proved  in  the  following  way.  If  an  electric  current  is 
passed  through  a  dish  of  water,  the  liquid  becomes  separated 
into  two  gases,  one  of  which  is  oxygen,  and  the  other  a  gas 
called  hy'dro-gen  (Greek,  hu'dor= water  +  gen  =  maker).  We 
find,  on  collecting  the  two  gases,  that  we  get  twice  as  great 
a  volume  of  hydrogen  as  of  oxygen.  Hence  we  represent  the 
composition  of 'water  by  the  symbol  H20,  which  means  that 
two  parts  of  hydrogen  are  combined  with  one  part  of  oxygen. 
That  such  a  combination  really  takes  place  can  be  demon- 


10 


STUDIES  IN  PHYSIOLOGY 


strated  by  holding  a  dry  tumbler  over  a  flame  of  burning 
hydrogen.1  The  gas  combines  with  oxygen,  and  drops  of 
moisture  collect  on  the  inside,  as  we  noticed  when  the  match 
wood  was  burned.  Water,  therefore,  may  be  called  an  oxid 
of  hydrogen. 

Oxidation.  —  Since  oxygen  is  always  necessary  for  the 
ordinary  processes  of  burning,  to  this  chemical  action  is 
given  the  general  name,  ox-i-da'tion.  It  may  take  place 
slowly,  as  is  the  case  when  we  rub  a  match  tip  over  our 
fingers,2  or  rapidly,  as  when  we  scratch  a  match  on  sand- 
paper. In  any  case  oxidation  means  the  chemical  union  of 
oxygen  with  some  other  substance.  It  is  always  accompanied 
by  a  certain  amount  of  heat,  and  often,  as  in  the  burning  of 
a  match  or  a  candle,  by  light. 

Air,  as  we  shall  soon  learn  (p.  13),  is  not  a  chemical  com- 
pound, but  a  mixture  of  two  gases ;  for  these  gases  do  not 
form  a  chemical  union. 

Most  of  the  facts  in  the  preceding  paragraphs  may  be 
summarized  in  the  following  outline :  — 

THE  BURNING  OF  A  MATCH 


Materials  in  a  Match  +  Oxygen  in  Air 

1.  Phosphorus  on  the  tip     -f  Oxygen 
(yellow,  waxy,  solid) 


2.  Sulphur  on  the  tip 
(yellow  powder) 


+  Oxygen     = 


+  Oxygen     = 


3.  Hydrogen  in  wood 

(colorless,  odorless, 
tasteless  gas) 

4.  Carbon  in  wood  -f-  Oxygen 

(black,  brittle,  solid) 

5.  Mineral  matter  in  wood 

(white  or  gray  powder) 


=  Compounds  Formed 

Oxid  of  phosphorus 
(white  fumes  of  peculiar 
odor) 

Oxid  of  sulphur 

(invisible  gas  of  suffocat- 
ing odor) 

Oxid  of  hydrogen  (water) 
(colorless,  odorless,  taste- 
less liquid) 

Oxid  of  carbon  (carbon  di- 
oxid)    (colorless,    odor- 
less, tasteless  gas) 
Ash  left  after  burning 
(white  or  gray  powder) 


1  See  "  Laboratory  Exercises,"  No.  5. 

2  Rusting  of  iron  is  a  good  example  of  slow  oxidation. 


LESSONS  IN   CHEMISTRY 


11 


2.   A  STUDY  OF  AIR 

Preparation  of  Oxygen.1 — In  the  preceding  study  of  match- 
burning,  frequent  reference  has  been  made  to  oxygen  as  one 
of  the  elements  found  in  the  air.  To  study  the  peculiar 
properties  of  this  gas,  we  must  obtain  it  in  a  free  state; 
we  can  readily  get  it  in  this  form  from  compounds  that  con- 
tain a  large  amount  of  oxygen.  One  of  these  is  the  ordi- 
nary chlorate  of  potassium. 


FIG.  1.  — Preparation  of  Oxygen. 

We  first  mix  some  of  the  white  crystals  of  this  chlorate 
of  potassium  with  about  one  third  this  amount  of  a  black 
powder  called  oxid  of  manganese.  Then  we  put  the  two 
into  a  test  tube  and  close  its  opening  with  a  stopper  through 
which  is  passed  a  bent  glass  delivery  tube  (see  Fig.  1).  The 
other  end  of  the  latter  dips  beneath  the  water  in  a  collect- 
ing tray.  When  heat  is  applied  to  the  test  tube,  the  white 
crystals  and  black  powder  are  made  to  give  up  some  of  the 
oxygen  which  they  contain.  The  gas  passes  through  the 
delivery  tube;  and  since  it  does  not  readily  dissolve  in 
water,  it  comes  off  in  bubbles  and  escapes  into  the  air. 

Atmospheric  Pressure.2 — Suppose  now  we  fill  a  wide- 
mouthed  bottle  with  water,  cover  the  top  with  a  square  of 
glass  (Fig.  1),  and  invert  it  in  the  tray  of  water,  removing 

1  See  "Laboratory  Exercises,"  No.  2. 

2  See  "  Laboratory  Exercises,"  No.  4. 


12  STUDIES  IN  PHYSIOLOGY 

the  glass  plate  from  the  month  of  the  bottle  when  it  is  just 
over  the  end  of  the  delivery  tube.  The  bottle  still  remains 
filled  with  water.  We  have  learned  (p.  6)  that  the  atmos- 
phere above  the  earth  is  about  fifty  miles  in  thickness.  On 
every  square  inch  of  the  earth's  surface  at  the  level  of  the  sea 
this  air  presses  down  with  a  weight  equal  to  about  fifteen  pounds. 
Hence  if  our  tray  happens  to  measure  seven  by  ten  inches 
(seventy  square  inches),  the  atmospheric  pressure  on  the 
surface  of  the  water  will  be  seventy  times  fifteen  pounds,  or 
ten  hundred  and  fifty  pounds,  which  is  over  half  a  ton.  It  is 
this  downward  pressure  of  the  air  on  the  surface  of  the  water 
that  keeps  the  bottle  filled,  since  the  glass  bottom  of  the  bottle 
prevents  a  like  downward  pressure  on  the  water  within. 

Collection  of  Oxygen.  —  If  now  we  continue  to  heat  the 
mixture  of  chlorate  of  potassium  and  oxid  of  manganese, 
the  bubbles  of  oxygen  will  rise  into  the  bottle  and  gradually 
displace  the  water.  When  the  bottle  is  filled  with  the  gas, 
we  close  it  with  the  glass  plate,  and  turn  it  right  side  up. 
After  we  have  filled  several  bottles  in  the  same  way,  we  are 
ready  to  determine  some  of  the  characteristics  of  this  most 
important  element. 

Physical  Properties  of  Oxygen.  —  %  physical  properties 
we  mean  those  characteristics  of  a  substance  that  can  be 
determined  by  the  senses.  If  the  experiment  described 
above  has  been  carried  on  slowly,  and  if  the  gas  is  passed 
through  bottles  of  water  and  caustic  soda,  the  oxygen  is 
seen  to  be  colorless;  when  we  lift  the  cover  and  smell  of  the 
gas,  it  is  found  to  be  odorless ;  and  by  inhaling  some  into 
our  mouth  we  learn  that  it  is  tasteless.  We  might  of  course 
expect  these  results,  since  fresh  air,  in  which  oxygen  is 
present,  is  likewise  colorless,  tasteless,  and  odorless. 

Chemical  Properties  of  Oxygen.  —  The  striking  chemical 
property  of  oxygen  is  shown  by  the  following  experiments. 
Let  us  set  fire  to  a  piece  of  wood  and  then  extinguish  the 
flame,  leaving  a  glowing  spark  at  the  end.  Carefully 
removing  the  glass  plate  from  one  of  the  bottles  of  oxygen, 


LESSONS  IN  CHEMISTRY  IB 

we  thrust  in  the  glowing  stick.  It  immediately  bursts  into 
flame  and  burns  brightly  until  all  the  oxygen  is  used. 
Brilliant  fireworks  can  be  made  by  burning  phosphorus  or 
sulphur  in  the  other  bottles  we  filled.  Even  a  steel  watch- 
spring,  or  piece  of  picture  wire,  if  the  tip  is  dipped  in  burn- 
ing sulphur,  catches  fire  in  pure  oxygen  and  throws  oft' 
flashing  sparks  of  burning  metal.  We  see,  then,  that  the 
most  important  chemical  property  of  oxygen  is  its  power  to 
make  things  burn.  When  any  combustible  substance  is 
heated  sufficiently,  the  elements  of  which  it  is  composed 
unite  with  the  oxygen,  and  thus  are  formed  the  compounds 
we  have  called  oxids. 

Preparation  of  Nitrogen.1  —  The  other  gas  found  in  air  is 
called  ni'tro-gen.    These  two  elements,  oxygen  and  nitrogen, 
are  not  chemically  united ; 
they  are  simply  mixed,  as 
we  might  mingle  sand  and 
sugar.    We  can  easily  take 
the  sugar  from  the  sand 
by   putting    the    mixture 
in  water ;  the  sugar  is  dis-        FlG  2  _  reparation  of  Nitrogen, 
solved,  while  the  sand  re- 
mains untouched.     Chemists  can  also  remove  the  oxygen 
from  a  certain  quantity  of  air,  leaving  free  nitrogen. 

The  materials  required  for  the  experiment  are  a  tray  of 
water,  a  wide-mouthed  bottle,  a  bit  of  phosphorus  the  size 
of  a  pea,  and  a  piece  of  cork  large  enough  to  float  the  phos- 
phorus on  the  water.  Placing  the  phosphorus  on  the  cork 
and  lighting  it,  we  quickly  cover  it  with  the  mouth  of  the 
bottle  in  such  a  way  that  the  rim  reaches  just  beneath  the 
surface  of  the  water.  The  phosphorus  burns  readily  for  a 
time,  and  the  bottle  is  soon  filled  with  the  white  fumes  of 
oxid  of  phosphorus.  When  all  the  oxygen  has  been  used, 
the  flame  dies  out.  As  we  watch  the  experiment,  the  white 
fumes  are  seen  to  be  gradually  settling  toward  the  surface 
1  See  "Laboratory  Exercises,"  No.  3. 


14  STUDIES  IN  PHYSIOLOGY 

of  the  water ;  at  length  they  disappear  altogether.  Mean- 
while the  water  has  been  slowly  rising  into  the  bottle. 
When  this  upward  movement  has  ceased,  we  cover  with  a 
glass  plate  the  mouth  of  the  bottle  and  quickly  turn  it  right 
side  up,  thus  keeping  within  the  bottle  the  water  that  arose 
from  the  tray. 

A  Test  for  Acids.1  —  Let  us  first  examine  the  water  we  have 
collected  in  the  bottle.  If  we  drop  into  ordinary  water  a 
bit  of  paper  treated  with  a  kind  of  vegetable  stain  called 
blue  litmus,  the  color  remains  unchanged ;  but  if  we  dip  the 
blue  paper  into  any  kind  of  acid  substance,  as  lemon  juice, 
or  vinegar,  the  color  becomes  red.  The  presence  of  acids, 
then,  may  be  readily  demonstrated  by  using  blue  litmus. 
When  we  test  in  this  way  the  water  we  obtained  in  the  pre- 
ceding experiment,  we  find  it  is  acid.  The  white  fumes  of 
oxid  of  phosphorus,  which  we  saw  settling  upon  the  surface 
of  the  water,  have  been  dissolved  and  have  made  the  water 
acid  in  its  properties. 

The  Composition  of  Air.  —  While  the  phosphorus  was  burn- 
ing, it  continually  took  away  oxygen  from  the  air  confined 
in  the  bottle  until  all  the  oxygen  was  used.  Hence,  after 
the  oxid  of  phosphorus  thus  formed  had  been  dissolved  in 
water,  a  space  was  left.  But  the  pressure  of  the  atmosphere 
on  the  surface  of  the  water  outside  the  jar  caused  the  water 
to  rise  and  fill  this  space  as  fast  as  the  oxygen  was  with- 
drawn. The  water,  therefore,  comes  to  occupy  the  space  in 
the  bottle  which,  at  the  beginning  of  the  experiment  was 
taken  up  by  oxygen.  If  we  measure  the  capacity  of  the 
bottle  and  then  measure  the  amount*  of  water,  we  see  that 
the  latter  takes  up  about  one  fifth  of  the  space  in  the  bottle. 
This  means  that  air  is  composed  of  about  one  fifth  oxygen 
and  four  fifths  nitrogen  (see  Fig.  3).  (Much  more  accurate 
results  can  be  obtained  if  a  piece  of  phosphorus  is  floated 
on  the  cork  and  allowed  to  oxidize  slowly  within  the  bottle 
of  air  for  two  or  three  days.) 

1  See  "Laboratory  Exercises,"  No.  7. 


LESSONS   IN  CHEMISTRY 


15 


Properties  of  Nitrogen.  —  On  applying  to  nitrogen  the 
same  tests  that  we  used  in  studying  oxygen,  we  find  the 
physical  properties  of  the  two  gases  are  very  similar.  Both 
are  colorless,  tasteless,  and  odorless  gases.  In  chemical 
properties,  however,  they  differ  widely.  When  we  thrust 
into  a  jar  of  nitrogen  a  glowing  splinter  of  carbon,  the  spark 
is  at  once  extinguished.  Burning  sulphur  is  affected  in  the 
same  way,  and  even  phosphorus  ceases  to  burn  as  soon  as  it 
comes  in  contact  with  nitrogen.  All  this  means  that  phos- 
phorus, sulphur,  and  carbon  will  not  combine  with  nitrogen 
as  they  do  with  oxygen.  In  fact,  nitrogen  may  be  character- 
ized as  the  least  active  of  all  elements.  It  does  not  readily 
unite  with  any  other  element,  and  the  compounds  in  which 
nitrogen  is  found  are  very  unstable.  Gunpowder  and  nitro- 
glycerin  owe  their  explosive  power  to  the  fact  that  the 
nitrogen  present  easily  loses  its  hold  upon  the  other  ingredi- 
ents. The  nitrogen  in  the  air  prevents  oxidation  from  going 
on  at  too  rapid  a  rate. 


COMPOSITION  OF  THE  AIR 

PROPORTION 
-OF  INGREDIENTS 
PHYSICAL  PROPERTIES 
OF  INGREDIENTS 


COLORLESS,  ODORLESS, 
TASTELESS  GAS. 


COLORLESS,  ODORLESS, 
TASTELESS  GAS. 


CHEMICAL  PROPERTIES 
OF  INGREDIENTS 


WILL  NOT  BURN 

WILL  NOT  MAKE  THINGS  BURN, 

USED  TO  DILUTE  THE  OXYGEN. 


WILL  NOT  BURN 

MAKES  THINGS  BURN  BY  COMBIN- 
ING WITH  THEM  TO  FORM  OXID8. 

FIG.  3.  —  Composition  of  the  Air. 


16  STUDIES   IN  PHYSIOLOGY 


3.   THE  CHEMICAL  COMPOSITION  OF  THE  HUMAN  BODY 

We  are  now  to  consider  the  application  of  some  of  these 
principles  of  chemistry  to  the  study  of  the  human  body. 
Chemists  have  accurately  determined  the  chemical  composi- 
tion of  the  various  parts  of  the  body,  and  we  will  discuss 
some  of  the  most  important  substances  that  have  been 
shown  by  analysis  to  be  present. 

Water.  —  The  great  importance  of  water  in  the  composi- 
tion of  living  substance  is  evident  from  the  fact  that  it 
'forms  about  62%  of  the  weight  of  an  adult  man.  Hence,  if 
all  the  water  were  removed  from  the  body  of  a  man  weighing 
one  hundred  and  sixty-five  pounds,  the  solids  that  remained 
would  weigh  but  a  little  over  sixty  pounds.  The  different 
organs  vary  greatly  in  their  percentage  of  water :  bones  con- 
tain about  22%,  muscles  have  75%,  and  the  kidneys  82  %. 

Mineral  Matters.  —  Mineral  matters  are  found  in  greatest 
quantity  in  the  bones.  When  we  burn  bones,  about  one 
third  of  the  weight  disappears,  the  remaining  two  thirds 
being  bone  ash,  which  is  the  mineral  matter.  Every  part  of 
the  body,  however,  contains  some  mineral  ingredients,  for 
when  muscle,  liver,  brain,  or  blood  is  burned,  in  each  case 
there  remain  some  traces  of  ash. 

Gases.  —  A  large  amount  of  the  gas  oxygen  is  taken  into 
the  lungs,  whence  it  is  distributed  to  all  the  organs  by  the 
blood.  We  shall  find  that  in  our  bodies,  as  well  as  in 
the  experiments  with  the  match  this  oxygen  performs  the 
all-important  function  of  causing  oxidation.  One  of  the 
products  of  this  oxidation  is  the  gas  we  have  already  con- 
sidered ;  namely,  carbon  dioxid.  If  we  blow  through  a  tube 
or  a  straw  into  a  glass  of  clear  limewater,  the  liquid  be- 
comes milky.  Our  breath  is  therefore  constantly  removing 
from  our  bodies  a  gas  exactly  like  one  of  those  formed  by 
burning  the  match. 

Fats.  —  The  amount  of  fat  in  the  body  varies  greatly  in 


LESSONS   IN   CHEMISTRY  17 

different  individuals,  but  it  is  always  present  in  some  quan- 
tity. Muscle,  however  lean,  contains  particles  of  fat;  fat 
constitutes  a  small  percentage  of  the  blood;  it  fills  the 
spaces  in  the  interior  of  bones ;  and  it  is  often  deposited 
in  considerable  quantity  in  the  deeper  layers  of  the  skin. 
When  fat  is  heated,  it  first  melts  to  a  liquid.  At  a  higher 
temperature  it  will  scorch,  and  the  black  residue  shows  the 
presence  of  carbon.  In  the  body  this  fat  is  burned  by  com- 
bining with  oxygen,  and  this  is  one  of  the  ways  in  which  we 
are  kept  warm.  If  we  were  to  eat  nothing  for  several  days, 
we  could  still  be  kept  warm  and  be  able  to  do  a  certain 
amount  of  work,  a  result  due  largely  to  the  slow  oxidation 
of  the  fat  stored  in  various  parts  of  the  body. 

Carbohydrates.  —  The  substances  we  know  as  starches  and 
sugars  are  made  up  of  the  three  chemical  elements,  carbon, 
hydrogen,  and  oxygen,  and  the  hydrogen  and  oxygen  of 
these  compounds  are  always  in  the  same  proportion  in 
which  they  occur  in  water  (that  is,  H20).  Hence  these 
compounds  are  called  car-bo-hy'  drates  (carbon +hy  dor  = 
water).  In  the  blood  and  other  animal  tissues  we  find 
some  of  the  carbohydrate  called  grape  sugar.1  Another 
carbohydrate,  known  as  animal  starch  or  glycogen,  is  found 
In  the  liver.2  Carbohydrates,  like  fats,  contain  a  large 
amount  of  carbon,  which  also  unites  with  oxygen.  A  sec- 
ond ingredient  of  both  of  these  classes  of  compounds  is 
hydrogen ;  it  readily  combines  with  oxygen  to  form  water. 
The  fats  and  carbohydrates  found  in  the  composition  of  the 
body  may  be  regarded  as  stored-up  fuel  which  can  be  drawn 
upon  in  case  of  need.  Like  the  engine,  we  are  kept  warm 
and  enabled  to  do  work  by  the  oxidation  of  fuel. 

1  The  chemical  composition  of  grape  sugar  is  represented  by  the 
chemical  formula  C6Hi206,  which  means  that  every  molecule  of  grape 
sugar  contains  six  atoms  of  carbon,  twelve  atoms  of  hydrogen,  and 
six  atoms  of  oxygen. 

2  Glycogen  is  comp6sed  of  six  atoms  of  carbon,  ten  atoms  of  hydro- 
gen, and  five  atoms  of  oxygen,  its  chemical  formula  being  C6H1005. 

c 


18  STUDIES  IN  PHYSIOLOGY 

Nitrogenous  Substances.  —  The  most  important  substances 
in  the  living  body  are  the  ni-trog'e-nous  compounds.  They 
are  all  characterized,  as  the  name  implies,  by  the  presence  of 
the  element  nitrogen  (symbol  N).  Some  of  these  com- 
pounds which  are  present  in  all  living  substance  are  known 
as  pro'te-ids  or  albuminous  substances.  Without  exception, 
proteids  consist  chiefly  of  the  elements  carbon,  hydrogen, 
oxygen,  nitrogen,  and  sulphur,  and  often  other  elements  are 
present  in  their  composition.  They  are  the  most  complex 
substances  in  the  body.1 

From  the  carbon  of  the  proteids  also  there  is  formed  by 
oxidation  the  waste  gas  carbon  dioxid,  which,  as  we  have 
demonstrated,  is  thrown  off  from  the  lungs.  Another  im- 
portant waste  compound  that  comes  from  the  oxidation  of 
proteids  is  a  substance  known  as  u're-a.  Urea  contains 
most  of  the  nitrogen  that  cannot  be  further  used  by  the 
body.  It  is  taken  from  the  blood  by  the  kidneys  and  forms 
the  principal  solid  constituent  dissolved  in  the  urine. 

The  summary  on  the  following  page  contains  in  brief  the 
principal  facts  we  have  learned  in  regard  to  the  chemical 
composition  of  the  body. 

1  The  composition,  for  example,  of  the  proteid  hem-o-glo'bin  (Greek 
hai'ma= blood)  which  gives  the  red  color  to  the  blood,  is  said  by  one 
chemist  to  be  CeooHgeoOngN^SsFe  (Fe  being  the  symbol  for  iron). 
This  formula  means  that  a  molecule  of  the  compound  hemoglobin 
consists  of  over  eighteen  hundred  atoms,  six  hundred  of  which  are 
carbon,  nine  hundred  and  sixty,  hydrogen,  etc. 


LESSONS  IN   CHEMISTRY  19 

THE  CHEMICAL  COMPOSITION  OF  THE  HUMAN  BODY 


SUBSTANCES 
FOUND 

FORM  OF  SUB- 
STANCE 

COMPOSED  OF 

WHERE  FOUND  IN  THE 
BODY 

A.   Compounds  found  in  the  body. 

1.  Water. 

Liquid. 

H  and  O 

In  all  parts  of  the 

(=H«0). 

body. 

2.  Mineral 

Solid  or  in  so- 

Salts of  po- 

Principally in  bones  ; 

matters. 

lution. 

tassium,  cal- 

found also  in  other 

cium,  etc. 

parts. 

3.  Fats. 

Solid  or  in  so- 

C, H,  and  O. 

In    muscles,    bones, 

lution. 

blood,  and  beneath 

the  skin. 

4.  Carbohy- 

Solid or  in  so- 

C, H,  and  0 

Principally  in  liver, 

drates. 

lution. 

(H  and  O  in 

blood,  and  muscles. 

proportion 

of  H20). 

5.  Proteids. 

Solid  or  semi- 

C,   H,   0,   N, 

In    all    living    sub- 

fluid. 

S,  etc. 

stance. 

B.   Element  causing  the  oxidation  of  the  body. 

6.  Oxygen. 

Gas. 

0. 

Supplied  from  lungs 

by    blood     to     all 

parts  of  body. 

C.  Products  of  oxidation  of  the  body  (=  waste  substances). 

7.  Water. 

Gas  or  liquid. 

HandO 

Thrown  off  from  body 

(=H20). 

by  lungs,  skin,  kid- 

neys. 

8.  Carbon 

Gas. 

C  andO 

Taken  by  blood  from 

dioxid. 

(=COa). 

all    parts   of    body 

to  lungs  and  skin, 

whence  it  is  given 

off. 

9.  Urea. 

Solid  (in  so- 

C, H,  O,  and 

Taken  by  blood  from 

lution)  . 

N. 

all  parts  of  body  to 

kidneys   and    skin, 

whence  it  is  given  off. 

CHAPTER   III 

A  STUDY  OF  LIVING  SUBSTANCE 

1.   THE  GENERAL  STRUCTURE  OF  ANIMAL  BODIES 

Vertebrates  and  Invertebrates.  —  All  animals  may  be 
divided  into  two  great  classes,  known  respectively  as  the 
ver'te-brates  and  the  in-ver'te-brates.  To  the  first  group  belong 
the  animals  that  have  a  backbone.  We  are  all  familiar 
with  common  vertebrates  like  fishes,  frogs,  snakes,  birds, 
and  cats.  Insects,  worms,  and  clams,  on  the  other  hand, 
have  no  backbone;  hence  they  are  called  invertebrates 
(i.e.  animals  without  vertebrse). 

Regions  of  the  Body.  —  In  man  and  in  most  other  verte- 
brates we  can  distinguish  the  head  and  neck  region,  the 
trunk,  and  the  four  ap-pend'ag-es  or  limbs  which  are  at- 
tached to  the  trunk,  namely,  two  arms  and  two  legs,  or,  as 
they  are  more  often  called  in  descriptions  of  the  lower  ani- 
mals, the  four  legs.  Since  frequent  reference  will  be  made 
in  the  following  pages  to  different  vertebrates  and  inverte- 
brates, we  must  become  familiar  at  the  outset  with  certain 
terms  that  will  locate  definitely  corresponding  regions  in  all 
animals. 

Man  walks  on  two  appendages  (the  legs)  ;  the  long  axis  of 
his  trunk  is  vertical ;  and  above  his  body  is  his  head.  But 
dogs  and  other  four-footed  animals  have  a  horizontal  trunk 
with  the  head  attached  in  front.  Hence  the  same  adjective 
cannot  be  used  to  describe  the  position  of  the  head  of  man 
and  of  quadrupeds.  Biologists  have,  therefore,  adopted  the 
term  an-te'ri-or  (Latin  an'te  =  before)  which  can  be  applied 

20 


A   STUDY  OF  LIVING   SUBSTANCE  21 

to  the  head  end  of  any  animal.  A  corresponding  term  pos- 
te'ri-or  (Latin  post  =  after)  refers  to  the  opposite  end  of  the 
body.  We  can  include,  for  instance,  under  the  term  anterior 
appendages  the  wings  of  a  bird,  the  front  feet  of  a  horse, 
and  the  arms  of  man,  since  all  these  appendages  are  located 
toward  the  head  end  of  the  trunk. 

The  descriptive  term  dor'sal  (Latin  dor1  sum  =  back),  when 
applied  to  vertebrates, 'always  designates  the  region  of  the 
body  in  which  the  backbone  is  found.  If  this  term  is  used 
in  describing  the  structure  of  invertebrates,  it  refers  to  the 
upper  surface  of  the  animal.  Ven'tral  (Latin  ven'ter  = 
belly),  on  the  other  hand,  designates  the  under  or,  in  man, 
the  front  surface.  Both  in  man  and  in  the  horse  the  mouth 
opening  is  on  the  ventral  surface  of  the  body,  even  though 
its  position  apparently  differs  so  much  in  the  two  animals. 

Organs.1  —  When  we  study  the  body  more  closely,  espe- 
cially its  interior,  we  find,  in  various  regions,  parts  that 
carry  on  special  kinds  of  work.  Within  the  chest  cavity  in 
the  upper  or  anterior  part  of  the  trunk  is  the  heart,  which 
forces  the  blood  through  the  body.  Here,  also,  are  the  lungs, 
which  take  in  oxygen  and  give  it  to  the  blood,  and  which 
remove  some  of  the  waste  matters  from  the  body.  Below 
the  heart  and  lungs,  or  in  other  words,  posterior  to  the  trans- 
verse muscular  partition,  called  the  di'a-phragm,  are  the 
stomach  and  the  intestines,  the  liver  and  the  pancreas,  all 
of  which  help  to  change  our  food  into  liquid  form.  Here, 
too,  are  the  kidneys  and  the  spleen.  All  these  and  other 
parts  of  the  body,  like  the  brain,  the  spinal  cord,  and 
the  hands,  are  called  organs.  An  organ  is  a  part  of  a  liv- 
ing body  that  has  some  special  work  to  do  :  this  special  work 
is  called  its  function.  Our  hands  are  organs,  because  with 

1  On  the  next  page  is  a*  figure  of  the  internal  organs  of  a  rabbit 
(Fig.  4).  In  this  figure  most  of  the  organs  enumerated  above  can 
be  identified ;  the  form  and  position  of  these  organs  in  the  human 
body,  however,  are  somewhat  different,  as  one  sees  after  studying  the 
figures  on  pp.  76,  99,  130,  and  255. 


22 


STUDIES  IN  PHYSIOLOGY 


FIG.  4.  —  The  Internal  Organs  of  a  Rabbit. 


A  =  cavity  of  the  chest. 
,  a  =  cut  ends  of  ribs. 
B  =  diaphragm. 
(7  =  ventricles  of  heart. 
D  =  auricles  of  heart. 
E  =i  artery  to  lungs. 
F  =  aorta  (artery  to  rest  of  body) . 
G  =  lungs,  collapsed. 
JI=part    of   covering   of   lungs 
(pleura). 


/=  lower  end  of  breast  bone. 
K  =  portion  of  body  wall  between 

chest  and  abdomen. 
L  —  liver,  lying  toward  left  of 

body. 

M=  stomach. 
N,  O  =  small  intestine. 

P  =  coecum  (part  of  intestine). 
Q  =  large  intestine. 


A  STUDY  OF  LIVING  SUBSTANCE  23 

them  we  take  hold  of  things  and  make  the  definite  move- 
ments required  in  writing,  drawing,  and  sewing. 

Tissues.  —  When  we  pinch  the  arm  and  the  hand,  we  feel 
the  hard  bones  that  form  their  skeleton.  We  can  raise  from 
the  bones  the  softer  fleshy  material  called  muscle.  By 
straightening  back  our  fingers  as  far  as  possible,  we  can  see 
and  feel  on  the  back  of  the  hand  the  tough  cords  or  tendons 
of  connective  tissue.  Run  a  clean  needle  point  into  the  finger ; 
blood  flows  and  we  feel  pain.  In  this  way  we  discover  two 
more  of  the  materials  of  which  our  hand  is  composed,  name- 
ly, blood  and  nerves.  All  these  parts  of  the  body  we  have 
enumerated  are  known  as  tissues.  For  the  present,  a  tissue 
may  be  defined  as  one  of  the  building  materials  of  which  an  organ 
is  composed  (see  p.  28). *  In  the  hand  we  have  evidence  of 
the  presence  of  bone  tissue,  muscle  tissue,  connective  tissue, 
blood  tissue,  and  nerve  tissue.  Other  kinds  of  tissue  will  be 
discussed  in  the  pages  that  follow. 

2.   CELLS,  THE  UNITS  OF  LIVING  SUBSTANCE 

When  we  have  considered  the  characteristics  of  the  tissues, 
we  can  go  no  further  in  our  study  of  structure  without  the  aid 
of  the  compound  microscope.  With  this  instrument  we  dis- 
cover that  the  tissues  are  by  no  means  the  simplest  parts  of 
an  animal.  In  order  to  get  a  clear  idea  of  the  units  of 
which  living  substance  is  composed,  let  us  turn  for  a  time 
from  the  study  of  the  human  organism  and  consider  some  of 
the  lowest  of  animal  forms. 

The  Amoeba.  —  The  material  for  our  work  is  best  obtained 
by  securing  some  of  the  mud  and  decaying  leaves  from  the 
bottom  of  a  pool  of  water.  When  we  come  to  examine  a 
drop  of  this  sediment  with  microscope  lenses  that  magnify 
two  or  three  hundred  times,  a  wonderful  scene  of  life  is 
revealed.  Our  attention  is  fixed  upon  a  multitude  of  minute 

1  It  is  important  to  bear  in  mind  that  a  tissue  is  not  necessarily  or 
usually  a  thin  membrane  like  tissue  paper  ;  bony  tissue,  for  instance, 
has  considerable  thickness  and  great  strength. 


24  STUDIES  IN  PHYSIOLOGY 

living  forms  that  hurry  across  the  field  of  our  vision  with 
bustling  activity.  Here  and  there  are  little  creatures  that 
move  more  slowly,  often  by  performing  a  "series  of  somer- 
saults. If  we  examine  the  drop  very  closely,  rod-shaped 
organisms  of  exceeding  minuteness  (bacteria,  see  p.  32)  be- 
come visible,  which  are  bumping  against  one  another  in  their 
tremulous  activity. 

The  special  object  of  our  search  in  this  whirlpool  of  life 
is  a  microscopic  animal  about  one  one-hundreth  of  an  inch 

in  diameter,  called  the 
a-mce'ba.  This  minute 
creature  is  a  droplet  of 
colorless,  semi-fluid  sub- 
stance, at  first  perhaps 
more  or  less  spherical  in 
form.  But  as  we  look  at 
our  specimen,  we  notice 
that  its  shape  is  chang- 
ing. On  one  side  some 
of  the  material  of  which 

FIG.  5.  -  An'  amoeba,  highly  magnified.      the  amoeba  is  composed 

c.vac  =  contractile  vacuole  (probably  for  IS   slowly   streaming  out 

excretion).  to  form  a  bulging  pro- 

£  =  SS2f£t  (pooped.)  Action  or  process.     This 

extension  is  called  a,  false 

foot,  which  may  increase  in  size  until  all  of  the  substance 
of  the  animal  has  passed  into  it.  By  pushing  out  these 
processes  in  front  and  pulling  up  its  body  matter  from 
behind,  the  amoeba  moves  slowly  from  one  part  of  the  slide 
to  another.  This  characteristic  method  of  locomotion  is 
known  as  amoeboid.  If  we  suddenly  jar  the  slide,  all  the 
semi-fluid  substance,  in  the  extended  false  feet  is  drawn 
back  toward  the  center  of  the  animal,  and  the  amoeba  again 
assumes  its  spherical  form. 

Structure  of  a  Cell.  —  The  amoeba  is  one  of  the  simplest 
of   living  creatures.     It  is  known  as  a  one-celled  animal. 


A   STUDY  OF  LIVING   SUBSTANCE 


25 


We  must  now  try  to  get  a  clear  idea  of  what  is  meant  by 
the  term  cell,  since  a  "knowledge  of  cell  structure  and  cell 
activity  is  absolutely  essential  for  a  clear  understanding  of 
biology.  If  the  amoeba  is  colored  with  certain  stains,  we 
can  see  a  darker  spot  in  the  center  to  which  is  given  the 
name  cell  nu'cle-us  (Latin  nucleus  —  a  small  nut).  The 
rest  of  the  animal  is  called  its  cell  body.  The  living  sub- 
stance of  which  nucleus  and  cell  body  are  composed  is 
now  universally  known 
as  pro'to-plasm.  A  cell, 
therefore,  in  the  biological 
sense  is  a  bit  of  protoplasm 
containing  a  nucleus.1 

Cells  of  the  Blood.— 
Keeping  in  mind  the 
facts  we  have  learned  in 
our  study  of  the  amoeba, 
we  will  now  return  to 
the  structure  of  the  hu- 
man body.  Let  us  first 
examine  with  the  micro- 
scope a  drop  of  fresh 
blood.2  We  soon  find 
it  is  not  the  simple  red 
liquid  it  seems  to  be; 
it  consists  of  solid  par- 
ticles, called  blood  cor'pus-cles,  floating  in  a  watery  liquid 

1  The  term  cell  was  first  used  in  describing  the  structure  of  plants, 
because  in  plant  tissues  the  protoplasm  is  inclosed  in  little  boxes  or 
rooms,  the  boundaries  of  which  are  called  cell  walls.     The  botanists 
who  first  used  the  term  cell  noticed   the  walls   before  protoplasm 
was  discovered.    The  cell  walls  of  plants  are  formed  of  cel'lu-lose, 
a  substance  resembling  starch.     Many  animal  cells  do  not  have  a  cell 
wall. 

2  The  blood  can  be  easily  obtained  by  tying  a  cord  tightly  about 
the  finger  and  then  pricking  it  with   a  clean  needle.    A   drop  is 
squeezed  out  upon  a  glass  slide  and  covered  with  a  thin  cover  glass. 


FIG.  6.  —  Blood  Corpuscles. 

a,  6  =  white    corpuscles    (nucleus   not 

seen). 

c,  d,  e  —  white  corpuscles  (nucleus  seen). 
r  =  red  corpuscles  (surface  view) . 
r'  —  red  corpuscles  (edge  view)   run 
together  in  piles. 


26  STUDIES  IN  PHYSIOLOGY 

known  as  blood  plasma.  Like  the  amoeba,  these  corpuscles 
are  single  cells.  Two  kinds  may  be  distinguished,  which 
from  their  color  are  known  as  red  and  white  corpuscles. 

There  are  three  hundred  to  seven  hundred  times  as  many 
red  corpuscles  as  white.  But  we  shall  consider  the  white 
corpuscles  first  because  of  their  similarity  to  the  amoeba 
both  in  structure  and  in  activity.  Each  corpuscle  consists 
of  a  minute  bit  of  protoplasm  in  which  is  imbedded  a 
nucleus.  These  blood  cells  have  also  the  characteristic 
amoeboid  movement.  By  this  method  of  locomotion  they 
can  creep  along  in  a  direction  opposite  to  that  of  the  blood 
current,  and  they  have  even  been  seen  forcing  their  way 
through  the  walls  of  small  blood  vessels  by  pushing  out 
false  feet.  They  then  wander  about  in  the  tissues  of  the 
body  and  do  us  great  service,  as  we  shall  see,  especially  in 
time  of  disease. 

The  red  corpuscles  have  no  power  of  independent  motion. 
They  are  circular  disks,  concave  on  both  surfaces.1  Some 
idea  of  the  minute  size  of  these  cells  may  be  gained  from  the 
fact  that  five  millions  of  them  are  floating  about  in  a  drop 
of  blood  the  size  of  a  pin  head.  There  is  no  nucleus  in  the 
red  corpuscles;  yet  we  consider  them  as  modified  animal 
cells,  since  they  are  formed  from  cells  having  a  nucleus. 

Cells  in  Other  Tissues.  —  If  we  examine  microscopically 
nerve  tissue,  muscle  tissue,  or  any  other  building  material  of 
animal  bodies,  we  find  each  and  all  of  them  to  be  composed 
of  cells.  These  vary  somewhat  in  size,  although  all  are 
microscopic.  As  we  shall  see  there  are  characteristic  forms 
of  cells  for  each  tissue ;  but  every  animal  cell,  so  far  as  we 
know,  has  a  cell  body  and  a  nucleus. 

Intercellular  Substance.  —  When  we  look  at  the  end  of  a 
fresh  soup  bone,  we  see  a  white  shining  tissue,  known  as 

1  A  good  model  of  a  red  corpuscle  can  be  made  from  clay  or  putty. 
Roll  a  small  mass  about  the  size  of  the  finger  tip  into  a  sphere, 
flatten  it  until  the  thickness  is  one  fifth  the  diameter  ;  then  pinch  the 
flattened  disk  between  the  thumb  and.  finger. 


A  STUDY  OF  LIVING   SUBSTANCE 


car'-ti-lage  or  gristle.     Placing  a  thin  section  of  this  cartilage 

beneath     the     micro- 
scope,    we    can     dis-  .-:,>.          }n 

tinguish  cells  looking 

somewhat    like   blood 

corpuscles.      The   nu- 
cleus and  body  of  each 

cell     become     visible 

when    the    tissue    is 

stained ;    but    instead 

of  floating  in  a  liquid, 

as  did  the  red  corpus- 
cles of  the  blood,  these 

cells  are  imbedded  in 

solid   cartilage.      The 

term       in'ter-cel'lu-lar 

substance  (Latin,  in'ter 

=  between  +  cel'lu-la  =  cell)  is  applied  to  this  tough  gristle 

which  is  a  product  of  the  cartilage  cells. 

Another  kind  of  intercellular  substance  is  found  in  bone 

tissue.     If  a  thin 
section 
bone  is 


;> 

FIG.  7.  — Thin  Section  of  Cartilage,  highly 
magnified. 

a  =  group  of  two  cartilage  cells. 
b  =  group  of  four  cartilage  cells, 
c  =  cell  body  of  cartilage  cell. 
m  =  intercellular  substance  (cartilage). 
n  =  cell  nucleus  of  cartilage  cell. 


with 
scope, 


a 

of  dried 
examined 
the  micro- 
tiny  spaces 


are  seen,  which, 
when  the  bone  was 
alive,  were  filled 
with  the  proto- 
plasm of  cells. 
These  bone  cells 
are  usually  more 
or  less  oval  in  out- 
line, but  the  proto- 
plasm of  each  cell  body  extends  outward  in  many  fine  irregu- 
lar processes  that  approach  closely  to  the  processes  from 


FIG.  8. —Thin   Section  of  Bone,   magnified  110 

times. 
Photographed   through  the   microscope.    Black 

irregular  spots  are  filled  with  the  bone  cells. 

White  spaces  between  are   formed  by  bony 

intercellular  substance. 


28 


STUDIES  IN  PHYSIOLOGY 


other  cells.  A  bone  section,  therefore,  looks  as  though  it 
were  filled  with  a  multitude  of  amcebas,  each  of  which 
has  extended  several  branching  false  feet.  Between  these 
irregular  bone  cells  is  the  hard  intercellular  substance  that 
gives  rigidity  to  this  kind  of  tissue. 

Definition  of  a  Tissue.  —  A  tissue  may  now  be  defined  as  a 
building  material  of  an  organ,  composed  of  cells  of  the  same 
kind,  together  with  more  or  less  intercellular  substance. 

3.   SOME  OF  THE  PROPERTIES  OF  PROTOPLASM 

Microscopic  Appearance. — Protoplasm,  when  examined  with 
the  highest  powers  of  the  micro- 
scope, appears  as  a  colorless,  semi- 
fluid substance,  in  which  are  usually 
seen  solid  particles  or  granules. 
The  nucleus  is  commonly  found 
near  the  center  of  the  cell  and  is 
composed  of  protoplasm  denser 
than  that  of  the  cell  body.  The 
appearance  and  consistency  of  the 
protoplasm  surrounding  the  nu- 
cleus, that  is  in  the  cell  body,  may 
be  well  represented  by  the  raw 
white  of  an  egg ;  but  in  making  this  comparison  one  should 
bear  in  mind  that  the  white  of  egg  is  not  living  substance. 

Chemical  Composition.  —  Living  substance  contains  a  large 
amount  of  water,  which  keeps  it  semi-fluid.  If  we  dry  pro- 
toplasm, we  kill  it.  While  the  amount  of  water  in  the 
different  tissues,  as  we  have  seen,  varies  considerably,  it  con- 
stitutes on  the  average  nearly  two  thirds  of  the  body  weight. 
The  most  important  constituents  of  living  cells,  however,  are 
the  proteids.  These  complex  substances  are  always  present 
in  protoplasm,  and,  so  far  as  we  know,  they  can  be  made  only 
by  protoplasm.  Particles  of  sugar,  fat,  and  other  food  sub- 
stances, are  usually  found  in  protoplasm  and  help  give  to 
the  cell  body  its  granular  appearance. 


FIG.  9.— Parts  of  a  Cell. 

p  =  protoplasm  of  cell  body. 
n  =  nucleus. 


A   STUDY   OF   LIVING   SUBSTANCE  29 

Production  of  Energy.  —  Between  a  working  locomotive  and 
our  bodies,  as  already  noted,  there  are  many  points  of  re- 
semblance. The  building  materials  of  an  engine  are  brass, 
wood,  glass,  and  iron ;  these  may  be  regarded  as  the  tissues 
of  the  machine.  A  combination  of  several  of  these  materials 
form  the  boiler,  the  wheels,  the  whistle,  and  the  headlight ; 
and  since  each  of  these  parts  of  the  engine  has  some  special 
work  to  do,  we  may  call  them  organs.  Again,  like  our  bodies, 
the  engine  must  be  continually  supplied  with  water  and  fuel 
in  order  to  do  its  work.  As  coal  is  burned  in  the  locomotive 
to  give  heat  and  power,  so  food  is  oxidized  in  animals  ;  and 
in  both  kinds  of  machines  waste  materials  are  formed  and 
thrown  off. 

Growth.  —  But  the  comparison  between  our  bodies  and  a 
locomotive  must  not  be  carried  too  far.  In  the  first  place, 
no  one  ever  knew  of  an  engine  to  begin  its  existence  as  a 
small  machine  and  then  to  increase  in  size  little  by  little 
until  its  weight  had  multiplied  twenty  times.  Yet  this 
is  true  of  the  human  body.  An  average  child  at  birth  weighs 
about  seven  pounds ;  the  weight  of  a  grown  man  commonly 
exceeds  one  hundred  and  forty  pounds.  None  of  the  coal 
and  water  put  into  the  engine  is  changed  into  the  brass,  iron, 
or  other  "  tissue  "  of  the  machine.  But  in  the  human  body 
a  great  part  of  the  food  we  eat  becomes  muscle,  bone,  and 
brain,  for  these  animal  tissues  in  some  unknown  way  can 
make  over  lifeless  food  materials  into  living  substance.  One 
of  the  most  striking  properties  of  protoplasm  is  this  power 
to  make  more  protoplasm,  or  in  other  words,  to  grow.  To 
this  process  is  given  the  name  as-sim-i-la'tion  (Latin  ad  = 
to  +  similis  =  like) ;  for  when  muscle  tissue,  for  example, 
takes  from  the  blood  its  supply  of  food,  the  latter  is  made 
by  the  muscle  into  protoplasm  like  to  itself. 

Repair — By  continual  use  parts  of  the  locomotive  become 
worn  or  broken,  and  the  engine  must  go  to  the  machine  shop 
for  repairs.  In  our  bodies,  too,  the  tissues  are  being  con- 
stantly worn  away.  Every  time  we  use  our  muscles  some  of 


30  STUDIES  IN   PHYSIOLOGY 

the  protoplasm  is  oxidized ;  every  time  we  think  or  exert 
our  will  power,  some  of  the  living  tissue  of  the  brain  is 
probably  changed  into  dead  waste  material.  But,  in  contrast 
to  lifeless  machines,  our  bodies  are  self-repairing.  The  food 
we  eat  not  only  goes  to  increase  the  size  of  the  body ;  it  also 
furnishes  material  to  make  good  the  wear  and  tear  of  every- 
day life. 

In  the  human  body,  then,  a  given  kind  of  food  substance 
may  at  one  time  be  used  for  the  growth  of  the  body ;  at  another 
time  it  may  serve  for  the  repair  of  the  tissues;  or  still  again, 
as  in  the  engine,  it  may  be  burned  to  keep  us  warm  and 
to  give  us  power  to  work.  The  processes  of  growth,  repair, 
and  the  production  of  energy  in  the  human  body  are  un- 
doubtedly extremely  complex.  •  Oxidation  is  probably  only 
one  of  the  processes  involved.  To  the  whole  series  of 
changes  by  which  food  is  transformed  into  protoplasm  or 
is  made  to  yield  energy  is  given  the  name  me-tab'o-lism 
(Greek  metabole  =  a  change). 

Cell  Division —  Since  cells  are  the  units  of  which  the 
body  is  composed,  it  is  evident  that  when  the  tissues  grow, 
cells  must  increase  either  in  size  or  in  number.  Biologists 
know  that  cells  remain  nearly  constant  in  size,  however 
large  the  body  may  grow.  The  number  of  cells,  however, 
increases  enormously  as  one  grows  from  childhood  to  adult 
life. 

The  formation  of  new  cells  can  be  watched  in  animals  like 
the  amoeba.  Some  little  time  before  division  is  to  take  place 
the  cell  ceases  to  move  about,  pulls  in  its  false  feet,  and  be- 
comes more  or  less  spherical  in  form.  Important  changes 
appear  first  in  the  nucleus.  It  gradually  assumes  the  form  of 
a  dumb-bell ;  the  knobs  at  the  end  of  the  dumb-bell  then 
draw  away  from  each  other,  until  finally  the  connection 
is  broken  between  the  two  halves  of  the  nucleus.  The 
amoeba  has  now  two  nuclei,  one  at  each  end  of  the  cell. 
Meanwhile  the  cell  body  has  been  assuming  a  more  or  less 
oval  form,  and  its  protoplasm  begins  to  divide  into  halves.  At 


A   STUDY   OF   LIVING   SUBSTANCE 


31 


the  end  of  the  process  the  "  mother  cell "  has  been  equally 
divided  into  two  "  daughter  cells,"  each  having  a  nucleus 
and  cell  body.  The  daughter  cells  now  move  about,  take 
in  food,  grow,  and  in  turn  divide.  The  amoeba  "  family " 
now  consists  of  four  "  granddaughter  cells.'7 

The  process  of  cell  division  in  many  of  the  human  tis- 


FIG.  10.  —  An  Amoeba  in  Successive  Stages  of  Division. 
The  dark  spot  is  the  nucleus.    The  light  spot  is  the  contractile  vacuole. 

sues  is  far  more  complicated  than  in  the  amoeba.  The 
essential  facts  are  true,  however,  in  almost  every  case  of 
cell  division.  They  are  these :  (1)  the  material  of  the 
mother  nucleus  is  divided  in  such  a  way  that  each  daughter 
cell  receives  exactly  one  half;  (2)  a  more  or  less  equal 
division  of  the  material  of  tne  cell  body  follows  j  (3)  this 


32 


STUDIES  IN  PHYSIOLOGY 


process  is  followed  by  a  period  of  assimilation  in  which 
both  daughter  cells  increase  in  size. 

Before  we  leave  this  discussion  of  living  substance,  it  will 
be  well  to  consider  the  single-celled  organisms  known  as 
bac-te'ri-a  or  germs,  since  they  have  most  important  rela- 
tions to  the  health  of  our  bodies.  Yeast,  too,  will  be  dis- 
cussed, because  of  its  interesting  physiology  and  because  of 
its  importance  in  connection  with  bread-  and  liquor-making. 

4.   A  STUDY  OF  BACTERIA  1 

Changes  caused  by  Bacteria.  —  If  milk  is  allowed  to  stand 
in  a  warm  room,  it  becomes  sour  to  the  taste,  and  it  thickens 

or  curdles.  Meat  that 
has  been  kept  for  a 
considerable  time  de- 
cays, giving  off  disagree- 
able odors.  We  know, 
too,  that  water  in  which 
flower  stems  have  been 
kept,  at  length  becomes 
putrid.  All  these,  and 
countless  other  changes, 
are  caused  by  bacteria, 
those  microscopic  organ- 
isms that  were  hardly 
dreamed  of  forty  years 
ago. 

Microscopic  Appear- 
ance of  Bacteria.  —  The 
thin  scum  formed  on 


FIG. 


which 


11.  —  Rod-shaped     Bacteria 
cause  Lock-jaw. 

Magnified  about  800  times.  Photographed 
through  the  microscope.  Some  of  the 
bacteria  have  an  oval  light  colored 
spore  near  one  end. 


scum 

the  top  of  all  stagnant 
water  consists  of  millions  of  bacteria.  When  we  examine 
with  the  highest  powers  of  the  microscope  a  bit  of  this 
scum,  these  micro-organisms  are  seen  to  have  several  differ- 


1  See  "Laboratory  Exercises,"  No.  49. 


A   STUDY  OF  LIVING   SUBSTANCE  33 

ent  forms.  Some  are  rod-shaped  (like  a  firecracker),  some 
are  spherical,  others  are  egg-shaped,  or  spiral-shaped  like 
a  corkscrew.  Each  bacterium  is  a  tiny  bit  of  translucent 
protoplasm,  inclosed  in  a  cell  wall  of  cellulose.  Thus 'far  no 
nucleus  has  been  discovered  in  any  kind  of  bacteria.  Be- 
cause of  their  cellulose  walls,  and  because  of  their  likeness 
to  certain  low  forms  of  green  plants,  biologists  now  regard 
these  organisms  as  plants  rather  than  animals. 

Some  of  the  rod-shaped  bacteria  have  one  or  more  long 
hairlike  projections  from  the  ends,  called  cil'-i-a,  which  give 
the  germs  still  further  resemblance  to  firecrackers.  These 
cilia  lash  about  furiously,  and  thus  drive  the  cells  through 
the  water.  The  spiral  bacteria  roll  over  and  over,  and  ad- 
vance in  a  spiral  path  like  a  corkscrew  or  spiral  spring. 
Other  forms  have  rapid  movements,  but  it  is  not  known 
how  they  are  accomplished. 

Size  of  Bacteria.  —  It  is  very  difficult  to  get  any  clear 
notion  of  the  extreme  minuteness  of  bacteria.  It  means  but 
little  to  say  that  the  rod-shaped  forms  are  one  five-thou- 
sandth of  an  inch  in  length.  The  imagination  may  be 
somewhat  assisted  if  we  remember  that  fifteen  hundred  of 
them  arranged  in  a  procession  end  to  end  would  scarcely 
reach  across  the  head  of  a  pin. 

Reproduction  of  Bacteria.  —  When  conditions  are  favor- 
able, the  production  of  new  cells  goes  on  with  marvelous 
rapidity.  The  process  is  something  as  follows.  The  tiny 
cells  take  in  through  the  cell  wall  some  of  the  food  materials 
that  are  about  them,  change  this  food  into  protoplasm,  and 
thus  increase  somewhat  in  size.  The  limit  is  soon  reached, 
however,  and  the  bacterium  begins  to  divide  crosswise  into 
halves.  The  mother  cell  thus  forms  two  daughter  cells  by 
making  a  cross  partition  (cell  wall  of  cellulose)  between  the 
two  parts.  If  the  daughter  cells  cling  together,  a  chain  or  a 
mass  is  formed.  Oftentimes  they  separate  entirely  from 
each  other.  In  either  case  the  whole  mass  of  bacteria  is 
called  a  colony. 


34  STUDIES   IN  PHYSIOLOGY 

It  usually  takes  about  an  hour  for  the  division  to  take 
place.  Suppose,  then,  we  start  at  10  o'clock  some  morning 
with  a  single  healthy  bacterium.  If  conditions  are  favor- 
able, there  would  be  two  cells  at  11  o'clock,  and  by  12 
o'clock  each  of  these  two  daughter  cells  would  form  two 
granddaughter  cells ;  the  colony  would  then  number  four 
individuals.  Should  this  process  continue  for  24  hours  or 
until  10  o'clock  on  the  day  after  the  single  bacterium  began 
its  race,  the  colony  would  number  16,776,216  bacteria.  "  It 
has  been  calculated  by  an  eminent  biologist,"  says  Dr.  Prud- 
den,1  "  that  if  the  proper  conditions  could  be  maintained,  a 
rodlike  bacterium,  which  would  measure  about  a  thousandth 
of  an  inch  in  length,  multiplying  in  this  way,  would  in  less 
than  five  days  make  a  mass  which  would  completely  fill  as 
much  space  as  is  occupied  by  all  the  oceans  on  the  earth's 
surface,  supposing  them  to  have  an  average  depth  of  one 
mile." 

Necessary  Conditions  for  the  Growth  of  Bacteria.  —  Such  start- 
ling possibilities  as  those  suggested  in  the  preceding  section 
fortunately  can  never  become  realities,  for  the  favorable 
conditions  to  which  we  have  referred  soon  cease  to  exist. 
Bacteria,  like  all  other  living  organisms,  require  food,  oxy- 
gen, moisture,  and  a  certain  degree  of  warmth.  Let  any 
one  of  these  conditions  be  withheld,  and  the  cells  either  die 
or  cease  to  be  active.  Sometimes,  when  food  or  moisture 
begins  to  fail,  the  protoplasm  within  each  cell  rolls  itself 
into  a  ball  and  covers  itself  with  a  much  thickened  wall. 
This  protects  it  until  it  again  meets  with  conditions  favor- 
able for  growth.  The  process  we  have  been  describing  is 
known  as  spore  formation;  the  tiny  protoplasmic  sphere  is 
called  a  spore,  and  its  dense  covering  a  spore  wall.  In  this 
condition  bacteria  may  be  blown  hither  and  yon  as  a  part  of 
the  dust.  They  may  be  heated  even  above  the  temperature 
of  boiling  water  without  being  killed.  When  at  length  they 

1  "  The  Story  of  the  Bacteria,"  by  Dr.  T.  Mitchell  Prudden.  G.  P, 
Putnam's  Sons,  N.  Y. 


A   STUDY   OF   LIVING   SUBSTANCE  35 

settle  down  on  a  moist  surface  that  will  supply  them  with 
food,  the  spores  burst  their  thick  envelope,  assume  once 
more  their  rod-shaped  or  spiral  form,  and  go  on  feeding, 
assimilating,  and  reproducing  their  kind. 

Many  forms  of  bacteria  feed  upon  dead  animals  and 
plants,  cause  them  to  decay,  and  thus  finally  convert  them 
into  carbon  dioxid,  water,  and  other  simple  compounds  that 
can  be  used  by  the  higher  plants.  In  this  way  these  micro- 
organisms are  of  incalculable  benefit  to  mankind  and  to  all 
forms  of  life,  for  they  keep  the  surface  of  the  earth  from 
becoming  a  vast  cemetery.  To  the  action  of  bacteria  also 
are  due  many  of  the  flavors  of  meats  and  cheese. 

Unfortunately,  however,  there  are  certain  germs  that  find 
favorable  conditions  for  growth  only  in  living  animal  tissue. 
Thus  the  bacterium  of  consumption  grows  in  the  lungs,  the 
germ  of  diphtheria  in  the  throat,  and  the  bacteria  that  cause 
typhoid  fever  in  the  intestines.  These  disease-producing 
germs  are  called  by  Dr.  Prudden  "Man's  invisible  foes." 
Yet  wonderful  progress  is  being  made  in  the  fight  against 
them.  We  have  learned  how  to  check  the  ravages  of  chol- 
era, typhoid,  and  diphtheria,  and  even  consumption  is  found 
to  be  a  preventable  disease.  Further  discussion  of  bacteria 
will  be  found  in  several  of  the  subsequent  chapters. 

5.   A  STUDY  OF  YEAST  AND  FERMENTATION1 

Changes  Caused  by  Yeast.  — A  small  piece  of  a  cake  of  com- 
pressed yeast,  mixed  in  a  spoonful  of  water,  forms  a  milky 
fluid  that  is  much  like  so-called  bakers'  or  brewers'  yeast. 
When  this  is  added  to  a  cupful  of  water,  in  which  a  spoon- 
ful of  molasses  has  been  dissolved,  one  has  a  convenient 
mixture  with  which  to  carry  on  experiments  in  fermentation.2 

1  See  "Laboratory  Exercises,"  No.  48. 

2  This  mixture  should  be  placed  in  a  loosely  stoppered  bottle,  for  if 
the  bottle  is  tightly  closed,  an  explosion  may  be  caused  by  the  pressure 
of  the  gas  that  is  formed. 


36  STUDIES  IN  PHYSIOLOGY 

If  the  yeast  mixture  is  set  aside  in  a  warm  place  (70  to  90 
degrees  Fahrenheit)  for  a  short  time,  it  begins  to  "  work," 
and  bubbles  of  gas  rise  to  the  surface.  At  the  end  of  several 
hours,  we  notice  that  the  sweetness  of  the  molasses  is  dis- 
appearing, that  the  mixture  begins  to  smell  sour,  and  that  a 
sharp,  biting  taste  is  becoming  evident.  All  these  changes 
are  caused  by  the  growth  of  living  yeast  cells. 

Now,  what  is  the  gas  that  is  formed  in  this  process,  and 
what  causes  the  changes  in  taste  and  odor?  To  answer 
these  questions  we  must  carry  our  experiments  still  further. 
When  the  mixture  is  "working"  well,  the  bottle  should  be 
tightly  closed  with  a  rubber  stopper,  through  which  extends 
one  arm  of  an  inverted  U-shaped  tube.  The  other  end  of  this 
tube  should  run  over  to  the  bottom  of  a  test  tube  half-filled 
with  limewater.  The  gas  that  has  been  rising  through  the 
yeast  mixture,  now  passes  through  the  U-tube,  and  as  it  comes 
in  contact  with  the  limewater,  the  latter  changes  to  a  milky- 
white  color.  This  proves,  as  we  have  seen  on  p.  8,  that  the 
gas  formed  during  the  growth  of  yeast  is  carbon  dioxid. 

Distillation.  —  After  "  working  "  a  day  or  two,  the  yeast 
mixture  will  have  a  strong  taste  and  odor.  A  part  of  it 
should  then  be  poured  into  a  glass  Florence  flask  (commonly 
used  in  the  chemical  laboratory  for  boiling  liquids),  and  the 
mouth  should  be  closed  by  a  rubber  stopper.  The  short 
arm  of  a  long  delivery  tube  should  be  passed  through  this 
stopper.  When  the  flask  is  heated  gently,  some  of  the  liquid 
is  changed  to  a  vapor.  If  the  delivery  tube  is  cooled  by  cov- 
ering it  with  cloths  wet  in  cold  water,  the  vapor  condenses 
into  a  liquid,  which  comes  from  the  end  of  the  tube  in  drops. 
This  operation  we  have  been  describing  is  known  as  dis-til- 
la'tion.  In  distilling  a  liquid,  we  first  convert  it  into  a  vapor, 
and  then  condense  this  vapor  into  a  liquid.  After  collecting  a 
few  spoonfuls,  the  liquid  should  be  slowly  distilled  a 
second  time.  Then  we  obtain  a  colorless  fluid  that  has  the 
distinct  smell  and  taste  of  alcohol.  It  burns,  too,  with 
a  pale  blue  flame. 


A  STUDY  OF  LIVING  SUBSTANCE 


37 


Fermentation.  —  And  so  we  learn  that  yeast,  as  it  grows  in 
the  molasses  mixture,  changes  the  sweet  substances  into  car- 
bon dioxid  and  alcohol,  a  process  that  is  known  as  alcoholic 
fer-men-ta'tion. 

Microscopic  Appearance  of  Yeast.  —  While  watching  the 
yeast  experiments,  we  see  on  the  bottom  of  the  bottle  a 
dense,  white  sediment.  If  we  examine  with  the  microscope 
a  bit  of  this  sediment,  we  find  that  it  consists  t>f  innumerable 
bodies  of  minute  size.  These  are  yeast  cells.  Each  cell  is 
more  or  less  egg-shaped,  and  is  composed  of  colorless  proto- 
plasm inclosed  within  a  wall  of  cellulose.  By  the  use  of 
special  stains,  a  nucleus  becomes  visible.  (The  spherical 
dots  seen  in  fresh  yeast  cells  are  known  as  "  vacuoles  "  and 
are  filled  with  a  color- 
less liquid.)  Yeast  is 
regarded  as  one  of  the 
lowest  forms  of  plant  life. 
Reproduction  of  Yeast. 
—  Most  of  the  cells  that 
we  are  looking  at  are 
not  separate  individuals, 
but  are  strung  together 
in  little  chains.  This 
fact  leads  us  to  a  discus- 
sion of  the  method  of 
reproduction  of  yeast. 
When  there  is  a  suffi- 
cient supply  of  food, 
moisture,  and  Oxygen,  Magnified  about  200  times.  Photographed 

through  the  microscope.  One  can  see 
single  cells,  mother-and-daughter  colo- 
nies, and  near  the  center  a  mother  cell, 
two  daughter  cells,  and  a  granddaughter 
cell. 


Fia.  12. —Yeast  Cells. 


and  when  the  tempera- 
ture is  favorable,  these 
living  plant  cells  begin 
to  feed  and  to  grow. 

They  soon  reach  their  full  size,  and  then  the  cell  wall  is 
pushed  out  at  the  side  by  the  growing  protoplasm.  In 
this  way  a  bud  is  formed.  This  continues  to  grow  and 


38  STUDIES   IN  PHYSIOLOGY 

soon  becomes  a  daughter  cell,  closed  off  from  the  mothei 
cell  by  a  wall  of  cellulose.  Meanwhile,  one  or  more  buds 
may  be  forming  on  the  outside  of  the  daughter  cells.  If  all 
these  cells  cling  together,  a  colony  is  formed  which  consists 
of  a  mother  cell  (largest  in  size),  one  or  more  daughter 
cells,  and  several  tiny  granddaughter  cells.  The  individual 
cells  are  easily  separated  from  one  another.  This  method  of 
reproduction  is  known  as  budding. 

Spore  Formation  is  a  second  way  in  which  yeast  reproduces 
itself.  When  conditions  become  unfavorable  for  further 
growth,  the  protoplasm  within  each  cell  separates  into  spores 
(usually  four),  and  since  these  bodies  are  well  protected  by 
thick  spore  walls,  they  may  be  blown  about  in  the  dust  of 
the  air.  If  they  happen  to  settle  upon  a  surface  that  supplies 
food  and  moisture,  these  spores  develop  into  yeast  cells. 
For  this  reason,  it  is  very  difficult  to  keep  sweet  substances 
from  fermenting,  unless  they  are  heated  to  a  high  tem- 
perature and  then  carefully  closed  from  the  air.  Alcoholic 
fermentation  is  always  due  to  the  action  of  yeast. 

Uses  of  Yeast. — The  action  of  yeast  in  bread-making  will 
be  discussed  in  the  next  chapter.  These  minute  organisms 
are  also  of  great  commercial  importance  in  the  manufac- 
ture of  alcohol  and  of  all  kinds  of  liquors.  We  have 
learned  that  yeast  cells  are  found  commonly  in  the  air. 
As  different  kinds  of  fruits  ripen,  they  are  usually  more 
or  less  covered  with  yeast  or  its  spores.  When,  there- 
fore, grapes  are  gathered  and  their  juice  is  pressed  out, 
the  sweet  liquid  is  soon  alive  with  the  busy  cells,  and  fer- 
mentation begins  at  once.  Wines  are  produced  in  this  way. 
In  the  so-called  light  wines  the  percentage  of  alcohol  is 
small  (5  to  12%);  in  heavy  wines  it  is  15  to  25%.  Cider 
is  produced  by  the  fermentation  of  apple  juice. 

In  the  manufacture  of  beer  and  of  other  malt  liquors,  bar- 
ley is  commonly  used.  The  grain  is  soaked  and  allowed  to 
sprout  for  a  short  time,  until  the  starch  is  changed  to  grape 
sugar.  The  barley  kernels  are  then  killed  by  heat  to  pre- 


A   STUDY   OF   LIVING   SUBSTANCE  39 

vent  further  changes,  and  the  grain  is  then  known  as  malt. 
When  this  is  put  into  water,  the  sugar  is  extracted.  Yeast 
is  then  added,  and  the  mass  ferments.  The  beer  thus  formed 
contains  2  to  5%  of  alcohol. 

Distilled  Liquors,  or  spirits,  are  obtained  from  wines  and 
other  fermented  liquors  by  the  process  of  distillation,  the 
principles  of  which  have  already  been  explained.  Brandy 
is  made  by  distilling  wine,  whisky  is  obtained  from  fer- 
mented corn  and  rye,  and  rum  is  manufactured  from  molas- 
ses. All  of  these  liquors  contain  a  large  percentage  of 
alcohol  (40  to  50%). 

Patent  Medicines.  —  In  the  issue  of  Nov.  8, 1902,  of  Ameri- 
can Medicine  are  found  the  percentages  of  alcohol  in  eleven 
of  the  widely  advertised  patent  medicines.  These  percent- 
ages run  from  17  +  %  (in  a  nerve  medicine)  to  44  -|-  °/0  (in 
one  of  the  "stomach  bitters").  These  "bitters"  contain 
ten  times  the  quantity  of  alcohol  found  in  beer}  and  are  even 
stronger  than  whisky  and  brandy.  Hence,  the  average 
drug  store,  where  these  patent  medicines  are  freely  sold, 
must  share  with  the  liquor  saloon  the  heavy  responsibility 
for  the  prevalence  of  the  drink  habit. 

THE  STRUCTURE  OF  THE  LIVING  HUMAN  BODY 

1.  Protoplasm  is  the  living  substance,  composed  largely  of 

proteid,  water,  and  mineral  matters.    These  compounds 
are  made  up  of  C,  H,  0,  N,  S,  P,  and  other  elements. 

2.  Cells  of  the  body  are  to  a  large  extent  composed  of  pro- 

toplasm, which  forms  the  cell  body  and  nucleus. 

3.  Tissues  of  the  body  are  its  building  materials,  composed 

of  cells  of  the  same  kind  with  more  or  less  intercellular 
substance. 

4.  Organs  of  the   body   are  composed  of   various  tissues, 

which  work  together  to  perform  some  special  function. 

1  See  also  "The  Use  of  Temperance  Drinks,"  pp.  344,  345,  by 
Professor  H.  P.  Bowditch,  in  "Physiological  Aspects  of  the  Liquor 
Problem."  Houghton,  Mifflin,  £  Co.,  Boston. 


40  STUDIES  IN  PHYSIOLOGY 

5.  An  organism,  like  the  human  body,  is  composed  of  organs, 
each  doing  its  special  work,  yet  all  working  together 
for  the  common  good.  Thus  the  hand  supplies  the 
organs  of  digestion  with  food ;  the  organs  of  digestion 
change  the  food  into  blood,  some  of  which  goes  to 
furnish  the  hand  with  the  materials  it  needs  to  do  its 
work. 

THE  FUNCTIONS  ^CABRIED  ON  BY  ALL  PROTOPLASM 

1.  Taking  in  of  food  materials. 

2.  Change  of  food  materials  to  protoplasm  (assimilation). 

3.  Taking  in  of  oxygen  (respiration). 

4.  Oxidation  of  food  materials  to  produce  heat  and  other 

forms  of  energy. 

5.  Giving  off  of  waste  materials  (excretion). 


CHAPTER   IV 
A  STUDY  OF  FOODS 

Why  Foods  are  needed  in  the  Body.  —  In  our  study  of  the 
composition  of  the  body  (pp.  16-19)  we  discussed  the  pres- 
ence of  water,  proteids,  fats,  carbohydrates,  and  mineral 
matters.  We  have  learned,  also,  that  in  the  presence  of 
oxygen  some  of  these  materials  are  oxidized,  thus  forming 
the  waste  substances  carbon  dioxid,  water,  and  urea.  Hence, 
if  the  body  is  to  continue  its  activities,  there  must  be  a  con- 
stant supply  of  new  material.  This  supply  we  obtain  in  our 
foods. 

Definition  of  a  Food.  —  The  three  most  important  uses  of 
foods  were  suggested  on  p.  30  in  the  preceding  chapter. 
Hence  we  may  say  a  food  is  any  substance  that  yields  material 
for  the  repair  or  growth  of  the  body,  or  that  supplies  the  fuel 
used  by  the  body  for  producing  heat  or  poiver  to  do  work. 

1.    THE  COMPOSITION  OF  FOODS 

Nutrients.  —  Our  common  foods  are  made  up  of  many 
different  compounds.  Bread,  for  example,  is  composed  of 
water,  salt,  starch,  sugar,  fats,  and  proteids.  Over  80%  of 
butter  is  fat;  the  other  20%  is  largely  water  and  salt. 
These  ingredients  of  food  that  can  be  used  by  the  body  are  called 
nutrients.  They  may  be  classified  as  follows :  (1)  proteids 
(known  also  as  albuminous  and  nitrogenous  foods),  (2)  fats 
(and  oils),  (3)  carbohydrates  (starches  and  sugars),  (4)  min- 
eral matters,  and  (5)  water.1 

1  By  some  writers  water  is  not  regarded  as  a  nutrient.  Since,  how- 
ever, it  is  an  essential  constituent  of  protoplasm,  it  may  well  be  named 
among  the  nutrients. 

41 


42  STUDIES   IN  PHYSIOLOGY 

Refuse. —  In  many  foods  there  are  ingredients  which  the 
body  cannot  use:  for  example,  the  hard  part  of  bones,  the 
peel  of  potatoes,  and  the  shells  of  eggs  and  of  oysters. 
These  substances  we  call  refuse. 

Explanation  of  Food  Chart.1  — The  folio  wing  chart  (Fig.  13) 
shows  the  percentage  of  each  nutrient  in  several  kinds  of 
food.  The  first  line  of  figures  at  the  top  of  the  chart  and 
the  vertical  lines  below  them  divide  off  the  various  per- 
cents ;  for  example,  10%,  20%,  70%,  etc.  In  preparing  the 
first  line  of  the  chart  (which  shows  the  composition  of 
round  beef  with  bone)  a  large  number  of  analyses  of  meat 
were  made  and  averaged.  In  each  analysis  a  slice  of  round 
beef  with  the  bone  was  carefully  weighed.  The  bone  was 
then  removed,  and  found  to  constitute  about  7%  of  the 
original  weight  of  the  meat.  This  fact  is  shown  011  the 
chart  by  the  length  of  the  black  line  representing  refuse, 
which  extends  from  93%  to  100%.  The  meat  itself  was 
then  thoroughly  dried  to  remove  the  water,  and  when  the 
residue  was  weighed,  and  the  various  analyses  were  com- 
pared, it  was  found  that  water  averages  over  60%  of  this  cut 
of  beef  (represented  on  the  chart  by  the  double  oblique  lines 
extending  from  about  33%  to  93%).  The  proteids  and  fats 
were  separated  by  special  methods,  and  the  mineral  matters 
were  obtained  as  ash  by  burning  the  beef.  The  chart  then 
shows  that  something  over  19%  of  round  beef  consists  of 
proteids,  about  12%  is  fat,  and  1%  more  or  less  is  mineral 
matter.;  while,  as  already  noted,  there  is  60%  of  water,  and 
something  over  7%  of  refuse  and  other  indigestible  matter. 

1  The  United  States  Government  has  provided  for  an  extensive  in- 
quiry into  the  food  and  nutrition  of  man.  The  work,  done  imder 
the  authority  of  the  Department  of  Agriculture  in  Washington,  has 
been  in  charge  of  Professor  W.  O.  Atwater  of  Wesley  an  University, 
Middletown,  Conn.,  in  whose  laboratory  the  enterprise  was  begun  and 
some  of  the  most  important  part  of  the  work  has  been  done.  The 
practical  results  of  this  inquiry  are  published  by  the  Department  of 
Agriculture* in  the  form  of  popular  bulletins  (see  p.  60).  Figures  13, 
15,  16,  17,  and  18  were  copied  from  these  publications. 


A   STUDY  OF   FOODS 


43 


^PROTEIDS  FATS 

MUSCLE 
MAKING 


FUEL    INGREDIENTS 


DRATES  MATTERS         NbTRiENTS 


BE™E 
NUTRIENTS- 


FIG.  13.  —  Percentage  of  the  Nutrients  in  Foods. 

Percentage  of  Nutrients  in  Foods.  —  By  looking  at  the 
chart1  one  can  easily  compare  the  percentage  of  the  nutri- 
ents in  the  given  foods.  In  the  composition  of  beef, 

1  See  "  Laboratory  Exercises,"  No.  16,  A. 


44  STUDIES  IN   PHYSIOLOGY 

mutton,  and  beans  nearly  20%  is  seen  to  be  proteids,  while 
butter  and  potatoes  contain  less  than  2%.  The  percentage 
of  fat  is  high  in  butter  (about  80  %)  and  in  many  other 
animal  foods  ;  it  is  hardly  present  at  all,  however,  in  the 
foods  derived  from  plants.  On  the  other  hand  the  carbohy- 
drates (starches  and  sugars)  are  usually  wanting  altogether 
in  animal  foods,  but  they  constitute  a  large  percentage  of 
the  foods  of  vegetable  origin. 

2.     TESTS   FOR  THE  NUTRIENTS 

With  the  help  of  a  few  chemicals  and  simple  apparatus 
it  is  easy  to  determine  the  presence  or  absence  of  each  kind 
of  nutrient  in  a  given  food.  These  tests  are  as  follows  :  — 

Tests  for  Proteids.1 — (1)  Many  proteid  substances,  like 
white  of  egg  and  lean  meat,  when  heated,  are  coagulated  or 
hardened  into  a  solid  mass.  (2)  If  the  temperature  is 
raised  still  higher  and  these  foods  are  scorched,  a  peculiarly 
unpleasant  odor  -is  noticed,  which  may  be  compared  to  that 
of  burning  feathers.  (3)  One  of  the  best  methods  of  de- 
monstrating the  presence  of  proteids  is  by  the  use  of  nitric 
acid  and  ammonia.  Some  of  the  food  to  be  tested  is  placed 
in  a  test  tube,  concentrated  nitric  acid  is  added,  and  the 
mixture  is  warmed.  If  the  food  changes  to  a  yellow  color, 
we  may  be  sure  of  the  presence  of  proteids.  After  wash- 
ing the  egg  with  water  and  adding  concentrated  ammonia, 
we  find  that  the  yellow  color  changes  to  a  deep  orange. 

Tests  for  Fats.2 —  (1)  A  simple  method  of  testing  a  given 
food  for  fats  is  by  heating  a  small  quantity,  and  then 
placing  it  on  a  piece  of  paper.  If  fat  is  present,  it  will 
make  a  translucent  grease  spot  on  the  paper.  (2)  Ether  or 
benzine,3  when  poured  upon  foods,  dissolves  the  fats,  and 

1  See  "  Laboratory  Exercises,"  No.  11. 

2  See  "  Laboratory  Exercises,"  No.  12. 

8  Caution  !  Ether  or  benzine  must  never  be  used  near  a  flame  or  a 
hot  stove,  since  the  vapor  of  these  substances  is  very  inflammable. 


A  STUDY  OF  FOODS  45 

when  these  solvents  evaporate,  the  fat  or  oil  is  left  be- 
hind. (3)  A  solution  of  osmic  acid l  stains  fats  brown  or 
black. 

Test  for  Starch.2 — An  iodine  solution3  always  turns  starch 
blue.  If  a  large  amount  of  starch  is  present  in  a  food  that 
is  being  tested,  a  deep-blue  color  is  produced  upon  the  ad- 
dition of  a  few  drops  of  iodine ;  if  the  percentage  of  starch 
is  small,  the  color  will  be  light  blue;  the  absence  of  a 
blue  color  shows  that  starch  is  not  present. 

Test  for  Grape  Sugar.4 — Many  different  kinds  of  sugars 
are  found  in  foods;  for  example,  cane  sugar,  beet  sugar, 
sugar  of  milk,  and  grape  sugar.  These  sweet  substances 
differ  more  or  less  in  chemical  composition.  In  our  physio- 
logical study,  grape  sugar  is  the  most  important,  and  its 
presence  can  be  proved  in  the  following  way.  A  little  of 
the  given  food  is  put  into  a  test  tube,  and  hot  water  is  added 
to  dissolve  the  sugar  if  present.  Some  blue  Fehling's  solu- 
tion 5  is  then  added  to  the  mixture  in  the  test  tube,  and  the 

1  Osmic  acid  is  very  expensive,  and  does  not  keep  well  in  solution 
unless  the  bottle  in  which  it  is  contained  is  perfectly  clean  and  is 
Kept  in  the  dark.     A  1%  solution  gives  more  satisfactory  results. 

2  See  "Laboratory  Exercises,"  No.  9. 

8  A  quart  (1000  cc.)  of  iodine  solution  is  made  by  dissolving  in  5  tea- 
spoonfuls  (40  cc.)  of  water  one  half  teaspoonful  (4  grams)  of  potas- 
sium iodide  and  one  fourth  this  amount  (1  gram)  of  iodine.  This 
solution,  when  thoroughly  mixed,  should  be  diluted  to  make  one  quart 
(1000  cc.).  In  a  clean  bottle  this  mixture  will  keep  indefinitely. — 
From  "Laboratory  Exercises."  Henry  Holt  &  Co. 

4  See  "  Laboratory  Exercises,"  No.  10. 

6  To  make  a  quart  (1000  cc.)  of  Fehling's  solution,  dissolve  3  tea- 
spoonfuls  (35.64  grams)  of  pure  copper  sulphate  (blue  vitriol)  in  a 
little  less  than  a  half-pint  (200  cc.)  of  water.  Make  a  second  solution 
by  dissolving  in  a  pint  (500  cc.)  of  water  twelve  heaping  teaspoonfuls 
(150  gr.)  of  Rochelle  salt  and  3  (5-inch)  sticks  of  caustic  soda  (50  grams). 
Mix  the  two  solutions  thoroughly,  and  dilute  with  enough  water  to 
make  a  quart  (1000  cc.).  Fehling's  solution  does  not  keep  for  any 
great  length  of  time,  and  hence  must  be  made  up  fresh  a  short  time 
before  it  is  needed.  It  is  more  convenient  to  prepare  it  in  small 


46  STUDIES   IN  PHYSIOLOGY 

whole  is  boiled.  If  grape  sugar  is  present,  the  blue  Feh- 
ling's  solution  will  be  changed  to  a  yellow,  a  deep  orange,  or 
a  brick-red  color ;  if  it  is  not  present,  none  of  these  colors 
will  be  formed. 

Test  for  Mineral  Matters.1 —  The  test  for  mineral  matters 
has  been  already  suggested  in  connection  with  the  match 
experiments.  If,  when  foods  are  burned,  ashes  are  left 
behind,  we  may  conclude  that  mineral  matters  are  among 
the  ingredients  of  the  foods  we  are  testing. 

Test  for  Water.2  —  The  water,  found  in  varying  quantities 
in  all  foods,  may  be  obtained  by  putting  the  food  into  a 
closed  dish,  from  which  passes  out  a  delivery  tube  like 
that  used  in  the  distillation  of  alcohol.  When  the  dish 
is  heated,  the  water  is  driven  off  as  vapor.  This  is  cooled 
as  it  passes  through  the  delivery  tube,  and  falls  in  drops. 
The  percentage  of  water  may  be  determined,  as  in  the 
case  of  the  round  beef,  by  weighing  the  food  before  and 
after  drying. 

Pure  Food  Laws.  —  One  of  the  most  important  laws  passed 
by  the  59th  Congress  of  the  United  States  was  that  which 
compels  every  manufacturer  of  foods  or  medicines  to  state 
on  the  label  the  composition  of  each.  Analysis  of  foods 
and  drugs  have  proven  that  hitherto  many  of  them  were 
largely  adulterated  by  cheap  and  often  injurious  compounds, 
put  in  to  increase  the  manufacturers'  profits.  Then,  too,  as 
already  stated,  many  patent  medicines  contain  high  per- 
centages of  alcohol  and  other  dangerous  drugs.  Under  the 
new  law  the  purchaser,  if  he  takes  the  trouble  to  read  the 

quantities  from  the  tablets  that  can  be  obtained  from  druggists,  or 
from  John  Wyeth  &  Brothers,  Chemists,  Philadelphia.  Before  making 
any  tests,  boil  a  small  quantity  of  the  Fehling's  solution  in  a  clean 
test  tube.  If  it  retains  its  transparent  blue  color,  it  is  ready  for  use  ; 
otherwise  a  fresh  supply  must  be  prepared.  —  From  "Laboratory 
Exercises."  Henry  Holt  &  Co. 

1  See  "Laboratory  Exercises,"  No.  13. 

2  See  "Laboratory  Exercises,"  No.  8. 


A   STUDY   OF  FOODS  47 

printed  label,  should  be  able  to  determine  exactly  what  he 
is  paying  for  and  putting  into  his  body. 

3.   How  PLANTS  MANUFACTURE  FOOD  MATERIALS 

Carbohydrates. — A  glance  at  Fig.  13  shows  that  carbohy- 
drates are  found  almost  wholly  in  foods  of  vegetable  origin. 
These  starches  and  sugars  are  probably  the  simplest  form 
of  organic  food  manufactured  by  plants.  We  shall  now  try 
to  understand  something  of  the  method  by  which  plants 
carry  on  their  all-important  work. 

Organs  of  a  Plant.  —  The  common  plants  with  which  we  are 
familiar — for  example,  dandelions,  and  maple  trees — consist 
of  three  important  organs,  namely,  roots,  stems,  and  leaves. 
The  root  system  is  usually  found  beneath  the  ground, 
firmly  holding  the  plant  to  the  soil.  Stems,  on  the  other 
hand,  commonly  rise  into  the  air  in  a  more  or  less  vertical 
direction,  and  serve  as  a  means  of  connection  between  the 
roots  below  and  the  leaves  that  are  attached  along  the  sides 
and  at  the  top  of  the  plant.  If  one  cuts  off  from  a  .living 
plant  a  small  leafy  branch,  and  puts  the  lower  end  of  the 
stem  into  red  ink,  he  will  see  after  a  time  traces  of  the  red 
ink  in  the  veins  of  the  leaf;  and  if  the  experiment  is  success- 
ful, every  one  of  the  fine  branches  of  the  veins  will  at  last 
be  filled  with  the  colored  fluid.  Cross  and  longitudinal  sec- 
tions of  the  stem  will  show  that  the  red  ink  has  been  carried 
up  through  little  tubes  called  ducts.  If  pieces  of  root  are 
experimented  upon  in  the  same  way,  similar  ducts  will  be 
found.  We  can  demonstrate  in  this  and  in  other  ways  that 
there  is  a  continuous  system  of  ducts,  beginning  at  the  tips 
of  the  roots,  running  up  the  stem,  and  branching  out  into 
the  leaves.  By  this  means  water  and  the  mineral  matters 
dissolved  from  the  soil  are  carried  up  the  stem  and  supplied 
to  the  leaves. 

Leaves,  as  we  all  know,  are  usually  green  in  color.  When 
we  examine  the  cross  section  of  a  leaf  under  the  microscope, 


48 


STUDIES  IN  PHYSIOLOGY 


(see  Fig.  14)  we  can  make  out  a  multitude  of  minute  rec- 
tangular objects,  the  leaf  cells,  each  being  surrounded  by  a 
thin  wall  of  woody  material.  Within  each  cell-wall  there  are 
numerous  minute  green  masses  known  as  chlo'ro-phyll  bodies 
(from  Greek,  meaning  leaf  green).  These  chlorophyll  bodies 
are  grains  of  the  cell  protoplasm,  having  a  peculiar  green 
substance,  by  the  help  of  which  they  are  enabled  to  carry 
on  the  manufacture  of  starch  in  the  presence  of  sunlight. 

Starch  Manufacture.  —  For  the  manufacture  of  starch,  the 
raw  materials,  carbon,  hydrogen,  and  oxygen,  must  be  fur- 
nished to  these  chlorophyll  bodies.  The  water  (H20)  that 


— epidermis  covering  upper  surface 
of  the  leaf. 


leaf  cells  containing  green  chlo- 
rophyll bodies. 


— epidermis    covering  lower  surface 

of  the  leaf, 
stoma  (one  of  the  openings  through  the  epidermis  into  the 

interior  of  the  leaf). 
FIG.  14.  —  Cross  section  of  a  leaf  very  much  magnified. 

comes  up  from  the  roots  supplies  the  necessary  amount  of 
hydrogen  and  oxygen.  The  carbon  is  obtained  from  the 
carbon  dioxid  found  in  the  air.  The  latter  passes  into  the 
leaf  through  the  outer  layer  of  cells  by  means  of  many 
little  openings  or  mouths  known  as  sto'ma-ta  (Greek  sto- 
mata  =  mouths).  In  some  unknown  way  the  chlorophyll 
bodies,  when  acted  upon  by  sunlight,  are  able  to  separate 
the  carbon  dioxid  into  oxygen  and  carbon  and  to  cause  the 
carbon  thus  obtained  to  unite  with  the  hydrogen  and  oxygen  * 

1  The  whole  process  may  be  represented  by  a  formula  something  as 
follows :  — 


A  STUDY   OF  FOODS 


49 


of  the  water  brought  up  from  the  roots.  Plants,  therefore, 
in  manufacturing  food  materials  that  are  useful  to  animals, 
take  the  waste  carbon  dioxid  and  water  that  are  thrown  off 
from  animal  bodies,  and  give  in  exchange  free  oxygen,  which 
is  essential  for  animal  life.  Hence,  without  plants  animal 
life  would  soon  cease  to  exist. 


FIG.  15.  — The  Potato  Plant,  showing  Potato  (shaded  dark)  from  which 
Plant  has  grown ;  also  the  New  Growth  of  Stems,  Leaves,  and  Potatoes. 

Storage  of  Starch  and  Sugar.  —  We  shall  see  later  that  in 
the  human  body  starch  can  easily  be  changed  to  sugar.  In 
plants,  too,  a  similar  process  is  carried  on,  and  sugar  can 
also  be  changed  to  starch.  Some  of  these  carbohydrates,  as 
soon  as  they  are  made,  are  used  by  the  plant  for  the  pro- 

6  parts  carbon  dioxid  +  5  parts  water  give  1  part  starch  + 12  parts  oxygen. 
Or  6  C02  (=  C6Oi2)  +  5  H2O  (=  H10O5)  give  1  C6Hi005  +  12  O. 

This  means  that  for  every  six  parts  of  carbon  dioxid,  five  parts 
of  water  are  needed.  During  this  process  a  large  amount  of  oxygen 
(equivalent  to  all  the  oxygen  in  the  carbon  dioxid)  is  given  back  to 
the  air. 


50  STUDIES   IN   PHYSIOLOGY 

duction  of  energy  and  in  the  process  of  growth.  In  many 
plants,  however,  considerable  quantities  are  stored  away  for 
future  use.  In  the  potato  plant,  for  instance  (see  Fig.  15), 
a  great  amount  of  the  starch  manufactured  in  the  leaves  is 
changed  to  sugar,  is  carried  down  beneath  the  ground  through 
the  tubes  in  the  stem,  and  is  there  stored  away  as  starch  in 
the  swollen  tubers  that  we  call  potatoes.  In  a  similar  way 
sugar  is  collected  below  ground  in  the  beet  root  and  above 
ground  in  the  stem  of  the  sugar  cane. 

Proteid  Manufacture. — Proteids,  as  we  have  already  learned 
(p.  18),  are  among  the  most  complex  of  chemical  compounds. 
In  addition  to  the  carbon,  hydrogen,  and  oxygen  found  in 
the  carbohydrates,  the  proteids  contain  nitrogen  and  sulphur, 
and  sometimes  phosphorus  and  other  elements  are  present. 
It  is  very  probable  that  plants  make  proteids  out  of  carbo- 
hydrates, the  additional  nitrogen,  phosphorus,  and  sulphur 
being  furnished  by  the  materials  that  are  carried  up  from 
the  soil  by  the  sap. 

4.   USES  OF  THE  NUTRIENTS 

The  processes  by  which  foods  are  changed  into  protoplasm 
and  by  which  they  supply  the  body  with  heat  and  muscular 
energy  are  extremely  complex.  Much  study,  however,  has 
been  given  to  the  subject,  and  we  are  now  reasonably  sure 
as  to  some  of  the  uses  of  the  different  nutrients. 

Uses  of  Proteids.  —  We  have  learned  that  proteid  is  the 
most  important  substance  found  in  protoplasm.  This  class 
of  nutrients  is  therefore  essential  for  the  growth  and  repair 
of  muscle,  nerve,  and  all  the  other  body  tissues.  It  is  clear, 
then,  that  milk,  meats,  bread,  beans,  peas,  oatmeal,  and 
other  foods  that  contain  considerable  amounts  of  proteid 
must  be  of  first  importance  in  the  nutrition  of  the  body, 
especially  during  its  period  of  growth,  although,  as  we  shall 
see  later,  it  is  probably  true  that  the  average  adult  eats  more 
than  is  necessary  of  this  kind  of  nutrient.  Proteids  can 


A   STUDY  OF  FOODS  51 

also  be  oxidized  in  the  body,  and  give  heat  and  muscular 
energy ;  but  the  chief  fuel  nutrients  of  food  will  be  discussed 
in  the  next  section. 

Uses  of  Fats  and  Carbohydrates.  —  Some  of  the  fat  we  eat 
is  stored  away  as  fatty  tissue  and  kept  for  future  use.  This 
tissue  gives  a  plump  outline  to  the  body,  acts  as  a  cushion 
for  many  organs,  and  helps  to  keep  our  bodies  warm  by  pre- 
venting the  heat  from  escaping,  and  by  being  oxidized  as  it 
is  needed.  Much  of  the  fat  in  our  foods,  however,  is  prob- 
ably oxidized  to  furnish  heat  and  power  without  being 
stored  within  the  body,  and  this  class  of  nutrients  furnishes 
fuel  in  a  most  concentrated  form.  This  is  the  reason  why 
the  inhabitants  of  cold  countries  eat  such  large  quantities 
of  fatty  foods.  The  starches  and  sugars  of  bread,  potato, 
fruits,  and  milk  are  also  used  as  fuel.  Portions  of  the  car- 
bohydrates are  changed,  too,  into  fat  tissue  and  stored  as  a 
reserve  of  fuel. 

Comparison  of  Uses  of  the  Nutrients.  —  We  have  seen  that 
all  of  the  nutrients  thus  far  studied  can  be  used  to  supply 
the  body  with  energy.  If  our  diet  is  deficient  in  any  one, 
the  others  supply  the  need,  and  are  burned  instead.  For 
growth  and  repair,  however,  proteids  are  absolutely  essen- 
tial ;  neither  sugar,  starch,  nor  fat  can  be  transformed  into 
this  essential  ingredient  of  protoplasm.  An  animal  soon 
dies  if  it  is  not  supplied  with  a  certain  amount  of  proteid. 

The  Relative  Fuel  Values  of  the  Nutrients.  —  We  have  made 
frequent  reference  to  the  use  of  food  in  giving  energy  to  the 
body.  By  means  of  an  apparatus  called  the  cal-or-im'e-ter 
(Latin  color  =  heat  -f-  metiri  =  to  measure)  it  is  possible  to 
determine  the  amount  of  heat  that  each  kind  of  nutrient 
will  produce,  or,  in  other  words,  to  measure  its  fuel  value. 
As  we  measure  the  quantity  of  food  by  the  pound  or  quart, 
so  its  fuel  value  is  computed  in  heat  units  or  cal'o-ries.  For 

1  A  calorie  is  "the  quantity  of  heat  necessary  to  raise  the  temper- 
ature of  a  kilogram  of  water  from  0°  to  1°  centigrade." — Century 
Dictionary. 


52  STUDIES   IN  PHYSIOLOGY 

practical  purposes  a  calorie1  may  be  roughly  described  as  the 
amount  of  heat  required  to  raise  the  temperature  of  a  pound  of 
water  through  four  degrees  Fahrenheit.  The  fuel  value  of  one 
pound  of  each  of  the  nutrients  is  as  follows :  proteids,  1820 
calories ;  carbohydrates,  1820  calories ;  fats,  4040  calories. 
On  comparing  these  figures,  we  see  that  proteids  and  carbo- 
hydrates have  equal  value  in  generating  heat,  while  the  fuel 
value  of  fat  is  two  and  a  half  times  as  great. 

The  heat-producing  power  or  fuel  value  of  each  of  the  foods 
(in  Fig.  13)  is  indicated  by  the  narrow  black  line  ;  the  second 
row  of  figures  at  the  top  of  the  chart  (400,  800,  etc.)  repre- 
sents the  number  *  of  calories.  Thus  the  fuel  value  of  a 
pound  of  milk  is  about  300  calories ;  a  pound  of  butter,  on 
the  other  hand,  will  generate  nearly  3500  calories  of  energy. 

Uses  of  Mineral  Matters  and  Water.  —  The  mineral  mat- 
ters like  the  phosphates  of  lime  and  magnesium  are  neces- 
sary for  making  bone.  Salt  is  used  in  large  quantities  by 
all  civilized  nations ;  it  makes  foods  more  palatable,  and  it 
is  important  in  the  processes  of  digestion.  Water,  as  we 
have  learned,  is  an  essential  constituent  of  protoplasm,  and 
hence  the  body  needs  it  constantly.  A  large  amount  is 
supplied  by  the  water  contained  in  our  solid  foods,  and  we 
get  the  rest  from  the  milk,  tea,  coffee,  and  from  the  water 
that  we  drink. 

5.   COOKING  OF  FOODS 

Importance  of  Proper  Cooking.  —  Some  of  our  foods,  like 
milk,  nuts,  and  fruits,  are  eaten  without  being  cooked.  The 
great  majority,  however,  before  they  are  taken  into  our 
bodies  are  changed  considerably.  It  is  important  for  us  to 
learn  the  essential  principles  of  good  cooking,  since  food, 
as  often  prepared,  loses  much  of  its  flavor,  becomes  more  or 
less  indigestible,  and  is  deprived  of  a  considerable  percent- 
age of  its  nutrition. 

Methods  of  cooking  Meats.  —  In  civilized  communities  meats 
are  rarely  eaten  raw.  They  are  usually  cooked  by  broiling, 


A   STUDY   OF  FOODS  53 

roasting,  boiling,  or  frying.  Frying  involves  the  use  of  fats. 
Since  the  average  American  is  said  to  eat  too  much  fat,  and 
since  frying  tends  to  make  foods  indigestible,  this  is  doubt- 
less the  poorest  method  of  preparing  meat,  and  hence  we 
shall  not  discuss  it  further. 

Reasons  for  cooking  Meats.  — The  reasons  for  cooking  meat 
are  these  :  (1)  proper  cooking  loosens  and  softens  the  fibers, 
thus  preparing  the  meat  for  mastication  and  for  the  action 
of  the  digestive  juices  ;  (2)  heat  kills  the  bacteria  and  other 
parasites  (tapeworms  and  roundworms  or  trichina)  that  are 
sometimes  found  in  foods  of  animal  origin;  (3)  cooking 
makes  the  meat  more  attractive  in  appearance  and  often 
improves  its  flavor ;  and  (4)  cooked  meat  is  more  completely 
digested.  It  is  probably  true,  however,  that  raw  or  partly 
cooked  meats  are  more  easily  digested ;  for  this  reason  rare 
meat  is  usually  given  to  invalids. 

Soups.  —  If  we  wish  to  obtain  nutritious  soups,  the  meat 
should  be  cut  into  rather  small  pieces  and  first  put  into 
cold  water  to  which  a  little  salt  has  been  added.  A  small 
proportion  of  the  albuminous  substances,  and  large  amounts 
of  so-called  "extractives,"  or  flavoring  matters,  are  drawn 
out  by  the  water  and  salt,  and  since  the  meat  is  in  small 
pieces,  a  considerable  proportion  of  the  mineral  matters  is 
thus  dissolved.  When  we  warm  the  mixture,  we  cause  the 
fats  to  melt,  and  when  it  is  boiled,  much  of  the  tough  con- 
nective tissue  is  made  more  or  less  soluble  by  being  turned 
into  gelatin.  The  soups  thus  obtained,  which  are  rich  in 
proteids,  fats,  and  mineral  matters,  are  made  more  palatable 
by  the  addition  of  vegetables  and  condiments. 

The  meat  which  is  left  after  the  soup  has  been  prepared 
is,  of  course,  more  or  less  tasteless.  Only  small  percent- 
ages, however,  of  the  nutrients  have  been  withdrawn ;  hence 
the  soup  meat  should  not  be  thrown  away,  but  should  be 
used  for  making  hash,  as  described  on  p.  59. 

Boiling  Meats.  —  When  the  meat  itself  is  to  be  eaten,  and 
the  broth  is  not  to  be  used,  the  whole  piece  should  be  plunged 


54  STUDIES  IN  PHYSIOLOGY 

into  boiling  water  for  a  few  moments.  In  this  way  the 
albumin  on  the  surface  is  quickly  coagulated,  and  the  crust 
thus  formed  prevents  the  loss  of  the  meat  juices.  The 
temperature  of  the  water  should  then  be  reduced  somewhat 
below  the  boiling  point  by  pushing  the  kettle  toward  the 
bapk  of  the  stove,  and  the  meat  should  then  cook  slowly 
until  it  is  done.  A  piece  of  meat,  when  cooked  in  this  way, 
is  tender  and  juicy  throughout.  If,  however,  the  water  is 
kept  at  the  boiling  point  (212°  F.),  the  meat  can  be  easily 
torn  apart,  but  the  fibers  are  found  to  be  hard  and  stringy. 

Stewing.  —  It  is  unfortunate  that  meat  stews  are  not  more 
highly  regarded  in  American  families,  for  by  this  method  of 
preparing  meat  all  its  nutritive  ingredients  are  used.  To 
make  a  good  stew  the  meat  should  be  cut  into  rather  small 
pieces  and  placed  in  cold  water.  Some  of  the  flavoring  mat- 
ters and  soluble  albumins  pass  out  into  the  broth,  making 
it  rich  and  nutritious.  When  the  stew  is  allowed  to  simmer 
for  several  hours  on  the  back  of  the  stove,  the  meat  itself 
becomes  tender  and  readily  digestible.  The  addition  of 
vegetables  makes  it  a  most  nourishing  and  palatable  dish. 

Roasting  and  Broiling. — The  best  method  of  cooking  meat, 
if  the  broth  is  not  desired,  is  by  roasting  or  by  broiling,  since 
smaller  percentages  of  the  nutrients  are  lost  than  is  the  case 
in  boiling.  The  outer  layer  of  albumin  must,  however,  be 
coagulated  at  once,  and  for  this  purpose  a  very  hot  fire  is 
needed.  When  the  piece  to  be  roasted  is  small,  the  high 
temperature  should  be  maintained  until  the  meat  is  cooked. 

A  large  roast,  on  the  other  hand,  after  the  outer  covering 
has  been  coagulated  requires  a  slower  fire  and  a  longer  time; 
meat  is  not  a  good  conductor  of  heat,  and  a  hot  fire  would 
scorch  the  outside  before  the  central  mass  could  become 
thoroughly  heated.  A  better  crust  is  formed  on.  the  outer 
surface  of  the  roast  if  the  meat  juices  (mostly  fat)  in  the  pan 
are  frequently  poured  over  the  surface  of  the  roast.  This  is 
called  "basting." 

Reasons  for  cooking  Vegetables.  —  The  starches,  which  we 


A   STUDY   OF  FOODS 


55 


have  learned  are  present  in  large  quantity  in  foods  of  vege- 
table origin,  are  usually  inclosed  in  cells,  the  walls  of  which 
are  formed  of  indigestible  cellulose.  Hence,  before  starch 
can  be  digested,  it  must  be  freed  from  this  cellulose  envelope. 
This  is  largely  accomplished  by  cooking,  which  causes  the 
starch  grains  to  swell.  The  cell  walls  are  broken  open  in 
this  way,  and  when  the  grains  burst,  a  larger  surface  is  ex- 
posed to  the  action  of  the  digestive  juices  (Figs.  16  and  17). 
This  is  strikingly  shown  in  popping  corn.  The  crust  of 
bread  is  more  easily  digested  than  the  softer  parts,  and 
toasting  bread  increases  still  further  its  digestibility,  because 
this  browned  starch  (sometimes  called  soluble  starch)  requires 
less  change  before  it  can  be  used  by  the  body. 

Boiling  Vegetables. — Experiments  have  shown  that  a  good 
deal  of  nutrition  is  lost  by  boiling  vegetables  in  water. 
Much  of  this  waste  can  be  avoided,  however,  if  one  heeds 
the  following  directions  :  (1)  Vegetables  should  be  cooked 
as  far  as  possible  in  their  peels,  for  these  outside  coverings 
keep  the  sugar,  proteids,  and  mineral  matters  from  being 


FIG.  16.  —  Cells  of  Raw  Po- 
tato with  Starch  Grains 
inclosed  in  the  Cellulose 
Walls. 


FIG.  17.— Cells  of  a  Potato 
well  steamed  and  mashed. 
Starch  Grains  have  been 
burst  by  the  Heat. 


drawn  out  by  the  water;  (2)  if,  however,  the  vegetables 
must  be  peeled  and  cut  up,  the  pieces  should  be  as  large 
as  possible,  as  a  smaller  surface  is  thus  exposed  to  the 
water;  (3)  the  amount  of  water  should  be  as  small  as 


56  STUDIES   IN  PHYSIOLOGY 

possible,  and  the  vegetables  should  be  cooked  rapidly,  in 
order  to  give  less  time  for  the  solvent  action  to  take  place. 
Bread  Making. — When  bread  is  made,  water  (or  milk), 
butter,  salt,  sugar,  and  yeast  are  added  to  flour.  After  the 
mixture  has  been  stirred  together,  a  sticky  mass  of  dough  is 
formed,  which  in  a  warm  place  begins  to  rise.  This  is  due 
to  the  fact  that  the  yeast  cells  change  the  sugar  into  alcohol 
and  carbon  dioxid.  Bubbles  of  gas  are  thus  imprisoned  in 
the  sticky  dough.  While  expanding  and  seeking  to  escape, 
they  make  the  solid  mass  porous.  After  the  bread  has  risen 
sufficiently,  it  is  kneaded  in  order  to  break  up  the  large  bub- 
bles and  in  order  to  distribute  the  gas  throughout  the  dough. 
When  the  bread  is  baked,  the  alcohol  and  carbon  dioxid  pass 
off  into  the  air,  leaving  the  bread  light  and  digestible. 

6.   DAILY  DIET 

Diet  required  by  Americans.  —  Many  investigations  have 
been  carried  on,  in  this  country  and  in  Europe,  to  determine 
the  amount  of  each  kind  of  nutrient  needed  per  day  for  the 
work  of  the  body.  The  conclusions  that  were  drawn  from 
this  study  are  represented  on  the  lower  two  lines  of  Fig.  18. 
According  to  these  conclusions  the  average  American,  when 
at  moderate  work,  requires  about  one  fourth  of  a  pound  of 
proteids  to  provide  for  the  growth  and  repair  of  the  body, 
and  a  quarter  of  a  pound  of  fat  and  a  pound  of  carbo- 
hydrates to  furnish  the  needed  energy.  This  is  about  the 
amount  eaten  by  a  man  of  average  appetite. 

Recently,  however,  at  the  Scientific  School  of  Yale  Uni- 
versity, some  very  careful  experiments  have  been  performed 
by  Professor  Chittenden  which  seem  to  prove  conclusively 
that  this  pound  and  a  half  of  solid  nutrients  for  each  day  is 
considerably  more  than  what  the  body  really  needs.  Dr.  Chit- 
tenden experimented  on  five  of  the  Yale  University  profes- 
sors, on  thirteen  soldiers  of  the  United  States  army,  and  on 
five  of  the  best  athletes  at  Yale ;  he  found  that  all  agreed 
they  could  do  better  physical  and  mental  work,  and  that,  too, 


A  STUDY  OF  FOODS  57 

without  any  loss  of  weight,  when  they  had  become  accus- 
tomed to  taking  less  than  half  their  ordinary  amount  of  food. 
In  several  instances  rheumatism,  biliousness,  and  other 
derangements  of  the  body  were  cured  by  this  restricted  diet. 
"  There  is  no  question,  in  view  of  our  results,"  says  Professor 
Chittenden,  that  people  ordinarily  consume  much  more 
proteid  food  than  there  is  any  real  physiological  necessity 
for,  and  it  is  more  than  probable  that  this  excess  of  food  is 
in  the  long  run  detrimental  to  health,  weakening  rather  than 
strengthening  the  body,  and  defeating  the  very  objects  aimed 
at." 

Necessity  for  a  Mixed  Diet. — By  comparing  the  proportions 
of  the  nutrients  suggested  for  the  daily  diet  with  the  com- 
position of  the  various  foods  given  in  Fig.  22,  one  sees  that 
in  none  of  them  are  the  nutrients  in  the  right  proportions. 
Cow's  milk  comes  the  nearest  to  being  a  perfect  food,  but  its 
percentage  of  carbohydrates  is  too  small;  if  we  were  to  feed 
upon  meat  alone,  we  should  get  too  large  an  amount  of 
proteid  s;  while  most  of  the  vegetable  foods  supply  an  ex- 
cessive amount  of  carbohydrates.  Hence,  a  well-balanced 
diet  should  consist  of  a  mixture  of  many  kinds  of  foods,  a 
conclusion  that  agrees  with  our  everyday  experience.  Vege- 
tarians may  be  right  in  their  contention  that  all  the  nutritive 
elements  of  food  are  found  in  vegetables,  but  the  great  pro- 
portion of  the  human  race  doubtless  secure  a  far  more 
healthful  diet  by  combining  the  animal  proteids  and  fats 
with  the  carbohydrates  furnished  by  plants. 

7.   FOOD  ECONOMY1 

Importance  of  Food  Economy.  — It  is  said  that  in  a  large 
proportion  of  American  families  more  than  half  of  the  total 
income  is  spent  for  food,  and  that  rent,  fuel,  clothing,  and 
all  other  expenses  must  come  from  the  remainder;  hence 
the  importance  of  the  study  of  food  economy.  The  average 
American,  however,  is  far  from  economical  in  the  matter  of 

1  See  "Laboratory  Exercises,"  No.  16,  B. 


58 


STUDIES   IN  PHYSIOLOGY 

PROTEIDS     FATS  CARBOHYDRATES 


BEEF,  ROUND 


BEEF,  SIRLOIN 


HAM,  SMOKED 


SALT  PORK,  VERY  FAT 


CODFISH,   FRESH 


CODFISH,  SALT 


MACKEREL,  SALT 


OYSTERS,  35  CTS.  QUART 
EGGS,  25  CENTS  DOZEN 


MILK,  7  CENTS  QUART 


CHEESE,  WHOLE  MlLK 


CHEESE,  SKIM  MILK 


WEIGHTS  OF  NUTRIENTS  AND  CALORIES  OF  ENERGY 
IN  25  CENTS'  WORTH. 


6000  CAL. 
I 


m  I  ,  I 


<1     I        I 


BS. 
CAU 


WHEAT  FLOUR 


WHEAT  BREAD 


STANDARD  FOR  DAILY  DIET  FOR  1 


MAN  AT  MODERATE  WORK 


t  ATWATER 


FIG.  18.  —  Pecuniary  Economy  of  Foods. 

foods  ;    in  the  first  place  Tie  wastes  money  in  buying  foods,  and 
in  the  second  place  wastes  the  nutrients  he  has  bought. 


A   STUDY   OF  FOODS  59 

Economy  in  the  Purchase  of  Foods.  —  We  have  already 
suggested  that  smaller  quantities  of  food  should  be  eaten  by 
the  average  American,  and  this  is  especially  true,  so  far  as 
animal  proteids  are  concerned,  for  meats  are  the  most  ex- 
pensive kind  of  food.  If  this  plan  were  followed,  a  large 
saving  in  the  year's  expenses  could  be  effected.  Fig.  18 
shows  the  weights  of  different  food  materials  that  can  be 
purchased  for  25  cents.  On  comparing  the  two  meats  at 
the  top  of  the  chart,  one  can  see  that  a  greater  fraction  of 
a  pound  of  solid  nutriment  can  be  obtained  by  spending  25 
cents  for  round  steak  than  could  be  secured  by  the  purchase 
of  sirloin.  Yet  the  latter  is  bought  even  in  very  poor  fami- 
lies, possibly  because  of  the  mistaken  idea  that  higher  prices 
insure  more  nutrition.  From  oysters  one  gets  less  of  the 
nutrients  than  from  any  other  food  represented  on  the  chart ; 
hence,  if  one's  income  is  small,  this  kind  of  food  should  be 
regarded  as  a  luxury,  seldom  purchased  except  in  case  of  sick- 
ness. Among  the  best  foods  for  the  growing  boy  are  graham 
or  corn-meal  bread,  the  cereals  (oatmeal,  rice,  etc.),  milk, 
meat,  fruit,  and  fish ;  they  are  economical  and  furnish  the 
required  nutrients  in  a  form  that  can  be  easily  digested. 

Waste  of  Food.  —  In  discussing  the  cooking  of  foods,  we 
suggested  some  of  the  ways  by  which  the  loss  of  nutritive 
ingredients  can  be  prevented.  We  waste  foods,  however,  in 
other  ways ;  for  instance,  we  often  throw  away  bones  and 
gristle,  regardless  of  the  fact  that  they  contain  a  consider- 
able percentage  of  proteids,  gelatin,  and  fat  from  which  one 
might  make  a  nutritious  soup.  It  has  been  found  that  large 
proportions  of  the  food  materials  still  remain  in  a  piece  of 
meat  after  it  has  been  used  for  soup.  A  most  delicious  and 
healthful  hash  could  be  prepared  by  chopping  this  soup 
meat  and  combining  it  with  vegetables.  The  garbage  pails 
of  most  kitchens  receive  far  too  large  a  percentage  of  the 
food  that  is  bought  for  the  household,  and  many  a  dollar 
would  be  saved  for  other  purposes  if  more  care  were  exer- 
cised to  prevent  this  waste. 


60  STUDIES  IN  PHYSIOLOGY 

The  food  problem,  then,  for  the  healthy  human  being  is 
this  —  how  to  obtain  the  largest  amount  of  good,  nutritious 
food  for  the  least  money.  To  this  problem  an  intelligent 
individual,  if  he  can  be  led  to  see  the  importance  of  the  sub- 
ject, will  devote  considerable  thought.  This  problem  can- 
not be  solved,  as  we  have  seen,  by  consulting  market  prices, 
for  often  the  highest-priced  foods  contain  small  percentages 
of  the  nutrients.  Neither  can  we  be  sure  of  a  good  supply 
of  foods  by  following  our  tastes.  To  many  people  cakes 
and  sweetmeats  are  more  appetizing  than  sandwiches  and 
cereals.  Yet  it  is  the  latter  that  supply  the  all-essential 
proteids. 

The  composition  of  various  foods  can  be  found  only  by 
chemical  analysis,  and  their  nutritive  value  can  be  deter- 
mined only  by  experiment.  Fortunately  these  analyses 
and  experiments  are  being  carried  on  by  the  United  States 
government.  The  results  are  published  in  the  Bulletins 
of  the  Department  of  Agriculture,  Washington,  D.C.,  many 
of  which  will  be  sent  free  to  any  address.  The  most  sug- 
gestive of  these  publications  are  "  Foods :  Nutritive  Value 
and  Cost  "  ;  "  Meats  :  Composition  and  Cooking  "  ;  "  Milk 
as  a  Food";  "Fish  as  a  Food";  "Sugar  as  a  Food"; 
"  Foods,  and  the  Principles  of  Nutrition." 


A  STUDY  OF  FOODS 


61 


REVIEW  OF  FOODS 


NAME  OF 
NUTRIENT 

TEST  FOR  NUTRIENT 

USES  OP  NUTRIENT 

FOODS  CONTAINING 
NUTRIENT 

Proteid 
(albumin, 
nitrogenous 
food). 

Coagulates  when 
heated. 
Smells  like  burn- 
ing feathers 
when  scorched. 
Turned  to  orange 
color  by  nitric 
acid    and    am- 

Necessary for 
the  manufac- 
ture of   pro- 
toplasm. 
When  oxidized 
produces 
energy. 

Meat,  eggs,  milk, 
cheese  (among 
animal  foods)  , 
and  beans,  peas, 
oatmeal    (vege- 
table foods). 

monia. 

Starch. 

Turned  to  a  blue 
color  by  iodine 
solution. 

Produces  energy. 
Transformed 
into  fat. 

Vegetable    foods 
(especially 
cereals). 

Sugar. 

Fehling's   solu- 
tion is  turned 
orange  or  red 
when  boiled 
with    grape 

Produces  energy. 
Transformed 
into  fat. 

Vegetable    foods 
(especially 
fruits)  ;    milk 
sugar  is  found 
in  milk. 

sugar. 

Fats  (or 
oils). 

Make  grease 
spots  on  paper. 
Dissolved     by 
ether  or  ben- 
zine. 
Turned  brown  or 

Produce  energy. 
Transformed 
into  body-fat. 

Animal  foods 
(especially 
butter,  pork, 
cheese),  nuts, 
cocoa,  chocolate. 

black  by  osmic 
acid. 

* 

Mineral 
matters. 

Left  as  ash  after 
food  is  burned. 

Help  to  form 
bone  and 

Common  salt; 
mineral  matters 

other  tissues. 
Aid  in  digestion. 

in  most  vege- 
table and  ani- 
mal foods. 

CHAPTER  V 

A  STUDY  OF   STIMULANTS,   NARCOTICS,  AND  POISONS 

1.   DEFINITION  OF  STIMULANT,  NARCOTIC,  AND  POISON 

Definition  of  a  Stimulant.  —  In  the  preceding  chapter  we 
have  discussed  those  substances  that  yield  material  for  the 
repair  or  growth  of  the  body,  or  that  supply  the  fuel  used 
by  the  body  in  producing  heat  or  power  to  do  work.  But 
in  addition  to  the  various  nutrients  that  can  be  used  for  one 
or  all  of  these  purposes,  we  often  take  with  our  foods  cer- 
tain substances  that  are  not  used  in  any  of  these  ways.  For 
example,  pepper,  mustard,  vinegar,  tea,  and  coffee  never  be- 
come a  part  of  our  living  substance,  nor  are  they  consumed 
in  any  considerable  amount  to  supply  us  with  energy. 
Hence,  we  cannot  regard  these  compounds  as  foods.  Most 
of  them,  however,  add  an  agreeable  flavor  to  our  foods,  and 
so  stimulate  our  appetites  and  aid  in  the  digestion  of  the 
real  nutrients. 

Most  of  these  compounds,  also,  do  no  harm  in  our  bodies 
if  taken  in  moderate  quantities,  and  so  we  cannot  regard 
them  as  poisons ;  for  the  Century  Dictionary  defines  a  poi- 
son as  "  any  substance  which,  introduced  into  the  living  organ- 
ism directly,  tends  to  destroy  the  life  or  impair  the  health  of 
that  organism" 

We  are  considering,  then,  a  class  of  substances  that  are 
neither  foods  in  a  strict  sense,  nor  are  they  poisons.  This 
sort  of  compounds  we  call  stimulants.  A  stimulant  is  any 
agent  that  temporarily  quickens  some  process  in  the  body. 
When  we  wish  to  quicken  the  activities  of  a  horse,  we  touch 
him  more  or  less  with  a  whip,  which  acts  like  a  stimulant. 

62 


STIMULANTS,   NARCOTICS,   AND  POISONS  63 

And  in  a  similar  way  we  may  rightfully  use  some  of  the 
substances  we  have  named  above,  if  we  make  sure  that  we 
use  these  stimulants  in  moderation.-  We  should  always  re- 
member, however,  that  a  stimulant  causes  only  temporary 
increase  of  activity,  and  that  if  we  apply  it  too  frequently 
or  in  too  great  quantity  to  a  horse  or  within  our  bodies,  it 
soon  loses  its  power  to  bring  about  even  a  temporary  in- 
crease of  activity,  and  that  then  it  comes  to  do  absolute 
harm. 

Definition  of  a  Narcotic.  —  Another  class  of  substances  that 
we  sometimes  use  has  an  effect  directly  opposite  to  that  of 
stimulants.  Ether,  morphine,  and  chloroform,  for  example, 
do  not  quicken  any  process  in  the  body,  as  do  stimulants, 
but  on  the  contrary  lessen  the  degree  of  activity.  Hence, 
instead  of  comparing  the  action  of  such  substances  to  that 
of  a  whip  on  a  horse,  we  may  liken  them  to  the  bit  and  reins 
when  they  are  used  to  check  the  motions  of  the  animal. 
Any  compound  that  acts  in  this  way  is  called  a  narcotic, 
which  we  may  define  as  "  any  substance  that  directly  induces 
sleep,  blunts  the  senses,  and  in  large  amounts  produces  com- 
plete insensibility" 

The  terms  stimulant  and  narcotic  that  we  have  just  de- 
fined naturally  suggest  a  discussion  of  the  use  and  abuse  of 
tea  and  coffee,  tobacco  and  alcohol,  and  to  that  discussion 
we  will  now  turn. 

2.   TEA  AND  COFFEE 

Use  and  Abuse  of  Tea.  — "  Tea  should  be  used  only  in 
the  form  of  an  infusion,  made  by  pouring  boiling  water 
upon  the  right  amount  of  tea  leaves,  and  allowing  it  to  stand 
a  short  while  to  l  draw.' ':  For  this  purpose  about  a  spoon- 
ful of  tea  should  be  used  to  every  cup  of  water.  Tea  should 
never  be  put  on  the  stove  to  boil,  for  two  reasons :  in  the 
first  place,  by  this  treatment  the  delicate  taste  and  odor  are 
lost ;  and,  in  the  second  place,  if  the  tea  infusion  is  boiled, 
the  tea  leaves  give  out  a  chemical  known  as  tan'nin}  which 


64  STUDIES   IN   PHYSIOLOGY 

tends  to  injure  the  lining  of  the  stomach.  For  these  reasons, 
too,  the  tea  "  grounds  "  should  never  be  used  a  second  time 
for  the  preparation  of  tea.  The  finest  and  most  delicate  por- 
tion of  a  tea  infusion  is  that  which  is  poured  off  within  three 
or  four  minutes,  for  this  will  be  found  to  have  the  best 
flavor  and  the  least  of  tannin  and  other  harmful  compounds. 

"  When  properly  made,  tea  in  moderation  is  a  wholesome, 
agreeable,  and  refreshing  stimulant  beverage,  particularly 
grateful  in  conditions  of  mental  or  physical  weariness. 
Used  in  excess,  it  exerts  a  harmful  influence  upon  the  ner- 
vous system,  arid  in  a  too  strong  form  injures  the  digestive 
organs."  The  foregoing  remarks,  quoted  from  Harrington's 
"Practical  Hygiene,"  apply  to  adults  rather  than  to  growing 
children  and  youths;  for  in  early  life  stimulants  of  every 
kind  should  be  avoided  as  much  as  possible,  as  they  tend  to 
interfere  with  the  healthful  development  of  protoplasm. 
We  should  remember  that  tea  is  in  no  sense  a  food,  and  so 
cannot  be  of  use  in  repair  or  growth  of  tissue;  both  of  which 
functions  are  of  prime  importance  during  the  first  twenty 
years  of  life. 

Use  and  Abuse  of  Coffee. — Most  that  has  been  said  in 
regard  to  tea  applies  equally  well  to  coffee,  except  that  in 
its  preparation  the  infusion  should  be  put  on  the  stove  and 
allowed  to  come  to  a  boil;  it  should  then  be  put  on  the  back 
of  the  stove  until  used.  "Coffee  acts  as  a  decided  stimulant 
to  the  nervous  system  ;  it  doubtless  enables  adults  better  to 
perform  hard  work,  and  diminishes  for  them  the  sense  of 
weariness;  "  but  in  the  diet  of  a  growing  child,  both  tea  and 
coffee  should  be  used  very  sparingly,  if  at  all,  since  they 
simply  excite  the  organs  to  unnecessary  activity. 


3.   TOBACCO 

Effect  of  Tobacco  on  Growth.  —  In  discussing  the  effects  of 
tobacco,  it  is  important,  as  was  the  case  with  tea  and  coffee, 
to  distinguish  between  the  results  of  its  use  by  the  young 


STIMULANTS,   NARCOTICS,   AND  POISONS  65 

and  by  adults.  Just  because  his  father  seems  to  be  using 
tobacco  without  apparent  harm  is  no  reason  why  a  boy  can 
safely  smoke.  We  have  already  called  attention  to  the  com- 
plex composition  of  protoplasm.  During  the  whole  period 
in  which  the  body  is  attaining  its  growth  this  living  sub- 
stance is  affected  far  more  appreciably  and  seriously  by 
the  use  of  stimulants  and  narcotics  than  is  the  case  later  in 
life. 

Tobacco  is  a  narcotic  in  its  effects,  that  is,  it  tends  to 
decrease  activity  and  likewise  growth.  That  such  is  its 
effect  during  early  life  has  been  abundantly  proven  in 
many  ways.  But  perhaps  the  most  conclusive  facts  are 
those  presented  by  actual  measurements  made  in  college 
gymnasiums.  Dr.  Hitchcock  of  Amherst  College,  who  has 
made  careful  measurements  of  college  students  for  a  good 
many  years,  finds  that  those  who  do  not  smoke  increase  in 
height  during  their  college  course  37%  more  than  those 
who  do  smoke,  and  in  chest  girth  this  difference  is  42% 
or  nearly  one  half  as  much  again.  Dr.  Seaver  of  the  Yale 
Gymnasium  finds  also  that  in  height  and  lung  capacity 
smokers  are  considerably  inferior  to  those  who  do  not  use 
tobacco. 

"  Whatever  difference  of  opinion  there  may  be  regarding 
the  effect  of  tobacco  on  adults  —  and  much  difference  of 
opinion  exists  —  there  is  almost  complete  agreement  among 
those  best  qualified  to  know  that  the  use  of  tobacco  is  in  a 
high  degree  harmful  to  children  and  youths.  Physicians, 
teachers,  and  others  who  have  much  to  do  with  boys  very 
generally  remark  that  those  who  begin  to  smoke  at  an  early 
age  very  seldom  amount  to  much.  Andrew  D.  White,  former 
President  of  Cornell  University,  sums  up  the  matter  as  fol- 
lows: '  I  never  knew  a  student  to  smoke  cigarettes  who  did 
not  disappoint  expectations,  or,  to  use  one  expressive  ver- 
nacular, "  kinder  peter  out."  I  have  watched  this  class  of 
men  for  thirty  years,  and  cannot  recall  an  exception  to  this 
rule.  Cigarette  smoking  serves  not  only  to  weaken  a  young 


66  STUDIES   IN  PHYSIOLOGY 

man's  body,  but  also  to  undermine  his  will  and  to  weaken 
his  ambition.'  r' 

Tobacco  and  Athletics.  —  One  of  the  rules  rigidly  enforced 
in  athletic  contests  is  that  all  candidates  must  abstain  from 
the  use  of  tobacco  while  in  training.  The  reason  for  this 
insistence  is  the  fact  that  tobacco  seriously  interferes  with 
the  action  of  the  lungs  and  heart;  hence,  those  who  smoke 
are  found  to  be  easily  "  winded  "  in  the  games. 

4.   ALCOHOL 

Alcohol  as  a  Possible  Food.  —  Like  the  carbohydrates 
and  fat,  alcohol  is  composed  of  carbon,  hydrogen,  and 
oxygen.1  Since  it  contains  no  nitrogen,  it  has  no  value 
in  the  processes  of  growth  and  repair;  in  other  words,  it 
cannot  be  made  into  protoplasm.  It  cannot,  therefore,  in 
any  sense,  like  meat,  milk,  and  eggs,  answer  as  a  complete 
food. 

Alcohol  we  know  can  be  burned  or  oxidized  in  stoves  or 
lamps  for  the  production  of  heat,  and  doubtless  in  a  few 
years  this  kind  of  fuel  will  be  widely  used  for  generating 
mechanical  energy  in  various  kinds  of  engines.  Professor 
Atwater  has  shown  that  alcohol  also,  if  used  in  sufficiently 
small  amounts,  may  produce  within  the  human  body  a  cer- 
tain amount  of  heat  and  muscular  power.  Indeed,  in  some 
cases  of  extreme  weakness,  especially  in  diseases,  alcohol  is 
regarded  by  some  eminent  physicians  as  necessary  for  sav- 
ing life. 

Not  all  the  leading  writers  on  physiology,  however,  are  in 
agreement  as  to  any  possible  food  value  of  alcohol,  and 
the  following  quotations  will  show  a  wide  diversity  of 
opinion. 

Professor  Adolph  Tick:  "We  may  unhesitatingly  desig- 
nate as  a  poison  any  substance  which,  introduced  into  the 
blood  in  comparatively  small  amounts,  causes  disturbances 

1  Its  chemical  composition  is  represented  by  the  symbol  CaHgOH. 


STIMULANTS,   NARCOTICS,    AND  POISONS  67 

in  the  functions  of  any  organ.  That  alcohol  is  such  a  sub- 
stance cannot  be  doubted.  ...  It  is  when  introduced  into 
the  blood  oxidized,  like  a  nutriment,  to  carbon  dioxid  and 
water,  and  this  oxidization  must,  of  course,  like  the  oxidiza- 
tion of  albumen,  fat,  or  sugar,  produce  heat.  .  .  .  Although 
the  relations  of  the  oxidization  of  alcohol  to  that  of  the  true 
nutriments  in  the  animal  economy  have  not  yet  received  a 
complete  physiological  explanation,  it  is  certain  that  alcohol, 
even  when  taken  in  moderation,  cannot  be  classed  among 
the  useful  nutriments." — "Die  Alkoholf rage, "  2d  ed., 
Dresden,  1895,  pp.  2-6. 

G.  Bunge:  "We  know  that  alcohol  is  mostly  oxidized 
in  our  body.  .  .  .  Alcohol  is  therefore,  without  doubt, 
a  source  of  living  energy  in  our  body.  But  it  does  not 
follow  from  this  that  it  is  also  a  nutriment.  To  justify  this 
assumption  proof  must  be  furnished  that  the  living  energy 
set  free  by  its  oxidization  is  utilized  for  the  performance 
of  a  normal  function.  It  is  not  enough  that  potential 
energy  is  transformed  into  living  energy.  The  trans- 
formation must  take  place  at  the  right  time  and  place,  and 
at  definite  points  in  definite  elements  of  the  tissues.  These 
elements  are  not  adapted  to  be  fed  with  every  sort  of 
oxidizable  material.  We  do  not  know  whether  alcohol  can 
furnish  to  the  muscles  and  nerves  a  source  of  energy  for 
the  performance  of  their  functions.  ...  In  general,  alco- 
hol has  only  paralyzing  properties,  etc." — "Lehrbuch  der 
Physiologischen  und  Pathologischen  Chemie,"  Leipzig, 
1894,  p.  124. 

T.  Lauder-Brunton :  "The  conclusion  to  which  all  evi- 
dence points  is  that  alcohol  is  a  food,  and  in  certain  circum- 
stances, such  as  febrile  conditions,  it  may  be  a  very  useful 
food;  but  in  health,  when  other  kinds  of  foods  are  abundant, 
it  is  unnecessary,  and,  as  it  interferes  with  oxidization,  it  is 
an  inconvenient  kind  of  food."  —  "Text-book  of  Pharma- 
cology, Therapeutics,  and  Materia  Medica,"  London,  1887, 
p.  768. 


68  STUDIES  IN  PHYSIOLOGY 

M'Kendrick:  "If  oxidized  even  to  a  small  extent,  and 
the  evidence  as  indicated  points  to  the  oxidization  of  by  far 
the  larger  proportion  of  it  (95%),  alcohol  must  be  regarded 
in  the  scientific  sense  as  a  food.  .  .  .  While,  therefore,  it  must 
be  classed  technically  as  a  food,  it  is  in  many  respects  an 
unsuitable  food  and  its  place  can  be  taken  with  great  ad- 
vantage by  other  substances.7'  —  "Physiology,"  Glasgow, 
1889,  p.  19  (Vol.  2). 

Halliburton:  "Alcohol  is  thus  within  narrow  limits  a 
food.  ...  It  is,  moreover,  a  very  uneconomical  food;  much 
more  nutriment  would  have  been  obtained  from  the  barley 
or  grapes  from  which  it  was  made.  The  value  of  alcohol 
within  narrow  limits  is  not  as  a  food,  but  as  a  stimulant, 
not  only  to  digestion,  but  to  the  heart  and  brain." — "Text- 
book of  Chemical  and  Pathological  Physiology,"  1891, 
p.  600. 

"  We  have,  thus,  one  group  of  physiologists  at  the  one 
extreme,  who  take  grounds,  more  or  less  strongly,  against 
any  dietetic  use  or  value  of  alcohol,  even  this  group  admit- 
ting that  it  is  not  fully  proved  that  alcohol  is  not  a  food. 
We  have  a  second  group  who  are  inclined  to  favor  moderate 
dietetic  use  of  alcohol,  tending  to  class  it  with  non-proteid 
foods,  but  still  maintaining  that  its  classification  as  a  food 
is  not  clearly  established.  ...  A  third  group  of  physiolo- 
gists and  pharmacologists,  whether  they  advocate  or  oppose 
its  use,  evidently  consider  recent  discussions  as  to  the  food 
status  of  alcohol  unnecessary  quibbling.  For  them  the 
evidence  is  sufficient  to  pronounce  alcohol  in  moderate 
quantities  a  food."  —  "Physiological  Aspects  of  the  Liquor 
Problem."  Houghton,  Mifflin  &  Co.,  1903. 

Alcohol  as  a  Stimulant,  a  Narcotic,  and  a  Poison.  —  Alcohol, 
then,  may  be  regarded  as  having  food  value  when  prescribed 
by  a  physician  in  case  of  sickness,  and  doubtless  it  can  be 
oxidized  in  the  body  to  supply  a  certain  amount  of  energy, 
if  it  is  taken  in  small  quantity  and  sufficiently  diluted.  But 
as  ordinarily  used  in  liquors,  alcohol  becomes  almost  always 


STIMULANTS,   NARCOTICS,   AND   POISONS  69 

either  a  stimulant  or  a  narcotic,  and  it  is  for  this  purpose 
that  it  is  taken,  not  for  its  possible  fuel  value. 

In  later  chapters  we  shall  discuss  the  affects  of  alcohol  on 
various  organs  of  the  body.  One  fact  should,  however,  be 
continually  emphasized,  namely,  that  even  if  it  should  be 
proved  that  alcohol,  when  used  by  adults  in  moderation, 
may  generate  a  certain  amount  of  energy,  still  this  is  an 
exceedingly  dangerous  compound  to  introduce  in  any  form 
into  the  diet  of  a  boy  or  girl.  In  the  first  place,  even 
more  than  tobacco,  it  interferes  with  the  healthy  growth  of 
protoplasm ;  and  in  the  second  place,  the  use  of  liquors  in 
moderation  by  a  great  many  people,  both  young  and  old,  is 
absolutely  impossible.  Men  never  become  drunkards,  pau- 
pers, and  criminals  by  taking  the  real  nutrients,  starch- 
sugar,  fats,  or  proteids,  nor  does  the  taste  for  any  of  these 
foods  become  uncontrollable,  as  is  so  often  the  case  with 
alcohol.  "  Till  he  has  tried  it,  no  one  can  be  sure  whether 
he  can  control  his  appetite  or  not.  When  he  has  ascer- 
tained the  fact,  it  is  often  too  late.  The  child  should  be 
taught  to  avoid  alcohol  because  it  is  dangerous  to  him. 
The  only  certain  safety  for  the  young  lies  in.  total  ab- 
stinence." 

We  have  found,  then,  that  the  effects  of  alcohol  on  the 
body  depend  very  largely  upon  the  quantity  taken ;  if  the 
amount  is  small,  .alcohol  may  possibly  be  regarded  as  a 
source  of  energy,  and  hence,  in  a  limited  sense,  as  a  food ; 
in  larger  amounts  it  increases  temporarily  the  activity  of 
the  organs  of  the  body,  and  then  it  becomes  a  stimulant ;  if 
still  larger  quantities  are  taken,  the  narcotic  effects  of  alco- 
hol are  shown  in  complete  intoxication ;  and  finally,  a  suffi- 
cient amount  may  be  consumed  to  poison  the  organs  and 
cause  death. 

No  one  who  begins  the  use  of  alcohol  expects  to  take  such 
an  amount  that  it  will  act  like  a  poison,  or  even  as  a  nar- 
cotic. There  is,  however,  a  constant  danger  that  he  will  do 
so.  But  even  if  he  does  not,  the  following  quotations  will 


70  STUDIES   IN  PHYSIOLOGY 

show  that  moderate  drinking  is  likely  to  injure  one's  chances 
in  business  and  to  shorten  what  insurance  men  call  one's 
"  expectation  of  life." 

Business  Argument  for  Total  Abstinence.  —  Eule  17,  New 
York  Central  &  Hudson  Eiver  R.  R.:  "  The  use  of  intoxicat- 
ing drink  on  the  road  or  about  the  premises  of  the  corpora- 
tion is  strictly  forbidden.  No  one  will  be  employed,  or 
continued  in  employment,  who  is  known  to  be  in  the  habit 
of  drinking  intoxicating  liquor." 

Rule  H,  New  York,  New  Haven  &  Hartford  R.  R. :  "  The 
use  of  intoxicants  by  employes  while  on  duty  is  prohibited. 
Their  habitual  use,  or  the  frequenting  of  places  where  they 
are  sold,  is  sufficient  cause  for  dismissal." 

Total  Abstinence  and  Life  Insurance.1  —  "  It  is  now  becoming 
generally  recognized  that  the  alcohol  habit  is  one  of  the 
main  factors  in  determining  length  of  life.  No  life  office  will 
knowingly  accept  the  proposal  of  any  one  known  as  a  hard 
drinker.  Evidence  of  a  very  striking  kind  is  rapidly  accumu- 
lating which  shows  that  even  the  moderate  use  of  alcohol  is 
prejudicial  to  health  and  longevity.  In  England  about  a  dozen 
life  offices  recognize  this  fact  in  one  of  two  ways  :  (1)  By  giv- 
ing a  reduction  of  premium  to  abstainers,  or  (2)  awarding 
them  a  larger  share  in  the  profits.  The  Scottish  Temperance 
Life  Insurance  Company  has,  from  its  formation  in  1883, 
worked  its  business  in  two  sections,  giving  total  abstainers  a 
reduction  of  ten  per  cent  in  their  premiums.  Last  year  the 
Sun,  one  of  the  oldest  life  offices,  established  in  1810,  opened 
a  special  section  for  abstainers,  giving  them  a  reduction  of 
five  per  cent  in  their  premiums.  .  .  .  The  experience  of  all 
temperance  life  offices  proves  the  enhanced  vitality  of  total 
abstainers.  This  makes  it  evident  that,  when  they  are  mem- 
bers of  a  general  life  office,  abstainers  have  to  pay  more 
than  their  fair  share  toward  meeting  demands  made  by  the 
higher  death-rate  of  the  non-abstainers."  —  London  Spectator. 

1  These  quotations  were  furnished  the  author  by  the  Equitable  Life 
Assurance  Society  of  the  United  States. 


STIMULANTS,    NARCOTICS,   AND  POISONS  71 

• 

"  Ten  years  ago  the  American  Temperance  Life  Insurance 
Association  was  formed  in  this  city  (K.Y.),  and  accepts 
nothing  but  total  abstinence  risks.  It  has  had  pronounced 
success,  and  has  paid  something  like  $  200,000  in  death 
claims.  President  Frank  Delano  states  that  the  results  of. 
their  business  show  that  the  ratio  of  their  death-rate  to  that  of 
general  risks  is  about  26  per  cent  in  favor  of  the  total  ab- 
stainer." —  WILLIAM  E.  JOHNSON. 

The  Cost  of  Intemperance.  — The  following  figures,  compiled 
by  the  League  for  Social  Service  of  New  York  City  from  the 
United  States  Census,  present  some  very  striking  facts  as  to 
the  cost  to  our  country  of  the  abuse  of  alcohol.  During  the 
year  1880  (and  the  same  figures  would  doubtless  hold  true 
for  any  other  year),  it  was  found  that  three-fourths  of  all  the 
pauperism,  one-fourth  of  all  the  insanity,  and  three-fourths  of 
all  the  crime  in  the  United  States  were  directly  caused  by 
intoxicating  drinks. 

The  Effect  upon  Dogs  of  Moderate  Drinking  of  Alcohol.  — 
During  the  years  1895  to  1900,  Dr.  Hodge  of  Clark  Univer- 
sity, Worcester,  Mass.,  carried,  on  some  very  instructive 
experiments  upon  dogs.  He  secured  four  spaniel  puppies, 
all  of  which  were  born  on  Washington's  Birthday,  1895  j  the 
two  males  were  brothers  and  the  females  sisters.  Dr.  Hodge 
carefully  watched  the  four  for  nearly  two  months  before  be- 
ginning his  experiments,  in  order  to  pick  out  the  two  most 
vigorous  animals ;  these  he  named  "  Tipsy  "  and  "  Bum," 
and  then  put  in  with  their  chief  meal  each  day  a  moderate 
amount  of  alcohol ;  it  was  not  enough,  however,  to  cause  any 
evidence  of  intoxication.  The  other  two  spaniels,  "Nig" 
and  "  Topsy,"  received  no  alcohol. 

For  over  five  years  these  dogs  were  studied,  and  important 
facts  were  learned  as  to  the  general  effect  of  alcohol  on 
physiological  processes.  Early  in  his  observations  it  became 
evident  to  Dr.  Hodge  that  the  dogs  that  were  receiving  the 
alcohol  were  far  less  playful  than  were  those  that  had  no 
alcohol  in  their  food.  To  measure  the  comparative  activity 


72 


STUDIES   IN  PHYSIOLOGY 


of  the  different  animals  he  attached  to  the  collar  of  each  dog 
a  Waterbury  watch  adjusted  in  such  a  way  that  it  would  tick 
once  each  time  the  animal  moved,  and  so  at  six  o'clock  each 
day  he  could  determine  and  set  down  the  record  made  by 
each  dog.  He  found  that  for  a  period  of  two  months  and 
more  "Bum"  was  only  71%  as  active  as  "Nig,"  while 
"Tipsy"  moved  about  only  57%  as  much  as  "Topsy  ";  in 
other  words  the  two  alcoholic  dogs  lost  25%  to  50%  of  their 
activity. 


Bum. 


Tipsy. 


Nig. 


Topsy. 


FIG.  19.  —  The  appearance  of  the  four  spaniels  six  months  after  the  ex- 
periments were  begun.  (Copied  from  "Physiological  Aspects  of  Liquor 
Problem,"  by  permission  of  Dr.  Hodge  and  of  Houghton,  Mifflin  &  Co.) 

A  second  series  of  experiments  was  made  to  determine 
the  comparative  endurance  of  the  four  dogs  and  their  ability 
to  accomplish  things.  The  animals  were  all  taught  to  retrieve 
a  rubber  ball  when  it  was  thrown  the  length  of  the  gymna- 
sium floor,  a  distance  of  100  feet.  At  each  trial  the  ball  was 
thrown  100  times,  and  a  record  was  kept  of  all  the  dogs  that 


STIMULANTS,   NARCOTICS,   AND  POISONS  73 

started  for  the  ball  and  of  the  one  that  succeeded  in  bring- 
ing it  back.  When  he  had  averaged  a  long  series  of  experi- 
ments, Dr.  Hodge  found  that  "  Bum  "  and  "  Tipsy  "  secured 
the  ball  only  about  half  as  often  as  did  "  Nig  "  and  "  Topsy  " ; 
the  two  alcoholic  dogs  also  gave  evidence  of  much  greater 
fatigue  during  the  trials. 

"  A  very  striking  result  of  the  entire  research,"  says  Dr. 
Hodge,  "  and  one  entirely  unexpected  on  account  of  the 
small  doses  of  alcohol  given,  has  been  the  extreme  timidity 


H'CMlV.CMil  If  01  MA  I  PA  ft 

t  mij 

"•    oobp €/*••";    OOOO.-V 
eecctt* 

C  C  •  I  1  t 

i»   •••  +  .  3 It 


€•  * 


Fia.  20.  —  Diagram  showing  Offspring  of  the  Two  Pairs  of  Dogs. 

of  the  alcoholic  dogs.  .  .  .  While  able  to  hold  their  own 
with  the  other  dogs  in  the  kennel,  the  least  thing  out  of  the 
ordinary  caused  practically  all  the  alcoholic  dogs  to  exhibit 
fear,  while  the  others  evinced  only  curiosity  or  interest. 
Whistles  and  bells,  in  the  distance,  never  ceased  to  throw 
them  into  a  panic  in  which  they  howled  and  yelped,  while 
the  normal  dogs  simply  barked.  This  holds  true  of  all  the 
dogs  that  had  alcohol  in  any  amount." 

Another  most  striking  result  of  the  use  of  alcohol  was 


74  STUDIES  IN  PHYSIOLOGY 

shown  in  its  effects  on  the  young  of  "  Bum  "  and  "  Tipsy." 
Of  the  23  puppies  descended  from  these  alcoholic  animals, 
only  17%  lived  to  be  normal  dogs;  the  rest  were  either  de- 
formed or  unable  to  nourish  themselves,  and  all  died  soon 
after  birth.  On  the  other  hand,  of  the  45  young  of  "  Nig  " 
and  "Topsy,"  over  90%  were  healthy  puppies.  (See  Fig. 
20.)  Hence,  the  puppies  of  the  dogs  that  took  alcohol,  even 
in  moderation,  were  over  Jive  times  as  likely  to  die  young 
as  were  the  puppies  born  of  abstaining  parents. 

In  the  spring  of  1897,  in  the  course  of  these  experiments, 
a  great  many  dogs .  throughout  the  city  of  Worcester  were 
afflicted  with  distemper,  and  dogs  sick  with  the  disease 
were  not  uncommon  on  the  streets.  At  that  time,  Dr.  Hodge 
had  in  all  five  dogs  that  were  taking  alcohol  and  four  that 
were  not.  It  was  found  that  there  was  a  marked  difference  in 
the  effect  of  the  disease  on  the  two  classes  of  animals.  All 
the  alcoholic  dogs,  with  the  exception  of  the  one  that  had 
taken  the  smallest  amount,  had  the  distemper  with  great 
severity ;  all  the  normal  dogs  had  it  in  the  mildest  possible 
form. 

Hence,  we  may  conclude  from  these  experiments  that  al- 
cohol, when  given  to  dogs,  even  in  moderation,  (1)  decreases 
their  natural  activity,  (2)  lessens  their  power  of  endurance 
and  their  ability  to  accomplish  things,  (3)  decreases  their 
power  of  resistance  to  disease,  and  (4)  increases  the  percent- 
age of  deformity  and  of  death  among  their  offspring. 
These  conclusions  have  a  most  important  bearing  on  the  gen- 
eral subject  we  are  considering,  for  statistics  show  that  pre- 
cisely similar  effects  follow  even  the  moderate  use  of  liquor 
by  human  beings. 


CHAPTER   VI 
A  STUDY  OF  BLOOD  MANUFACTURE 

Definition  of  Digestion.  —  In  the  preceding  chapter  we  dis- 
cussed the  composition  of  foods,  the  methods  of  cooking, 
and  the  uses  of  foods  to  the  body.  We  shall  now  follow 
the  changes  that  take  place  in  these  foods,  for  before  the 
different  nutrients  can  be  supplied  to  the  brain,  the  muscles, 
or  the  bones,  they  must  be  changed  from  a  solid  or  semi-fluid 
condition  into  liquids  that  can  be  absorbed.  This  process  is 
called  digestion.  It  is  carried  on  within  our  bodies  in  a 
complicated  tube  nearly  thirty  feet  in  length,  which  is 
called  the  al-i-men'ta-ry  canal  (Latin  alimentum  =  nourish- 
ment). Digestion,  then,  may  be  defined  as  the  series  of  changes 
within  the  alimentary  canal  by  which  food  is  made  ready  to 
become  a  part  of  the  blood. 

Parts  of  the  Alimentary  Canal.  —  The  alimentary  canal  be- 
gins at  the  mouth  opening,  enlarges  to  form  the  mouth  cavity, 
and  this  in  turn  communicates  behind  with  a  somewhat  smaller 
throat  cavity.  Posterior  to  the  throat  is  the  e-soph'a-gus  or 
gullet,  which  conducts  the  food  into  an  enlarged  pouch, 
the  stom'ach.  Most  of  the  lower  half  of  the  trunk  is  filled 
with  the  much  coiled  in-tes'  tine,  which  begins  at  the  stomach 
and  opens  to  the  outside  of  the  body  at  the  posterior  end  of 
the  trunk. 

Digestive  Glands.  —  Several  important  organs,  called  diges- 
tive glands,  lie  adjacent  to  the  alimentary  canal,  but  con- 
nected with  it.  They  produce  digestive  juices,  which  flow 
into  the  food  canal  through  small  pipes  or  ducts.  The  sal'- 
i-va-ry  glands  pour  their  secretions  into  the  mouth  cavity. 

75 


76 


STUDIES  IN  PHYSIOLOGY 


In  the  region  of  the  stomach  are  the  liver  and  the  pan'cre-as. 
The  former  secretes  bile  and  the  latter  pancreatic  juice. 
Both  of  these  digestive  juices  flow  into  the  intestine  in  the 


FIG.  23.  —  Parts  of  the  Alimentary  Canal. 

region  near  its  opening  from  the  stomach.  TJie  alimentary 
canal  may  be  regarded  as  a  blood-making  laboratory,  in  which 
our  food  is  made  liquid  by  the  juices  produced  in  the  digestive 
glands. 


A   STUDY   OF  BLOOD  MANUFACTURE  77 

1.  THE  MOUTH  CAVITY  1 

Walls  of  the  Mouth  Cavity.  —  The  cavity  of  the  mouth  is 
inclosed  at  the  sides  by  the  muscles  of  the  cheek.  The  roof 
of  the  mouth  is  formed  by  a  horizontal  plate  of  bone  (easily 
felt  by  the  finger  or  the  tongue),  called  the  hard  palate. 
This  separates  the  cavities  of  the  mouth  and  nose.  Near 
the  back  of  the  mouth  the  hard  palate  ends  abruptly,  and 
the  partition  between  these  two  cavities  is  completed  by  the 
soft  palate.  The  muscular  tongue  helps  to  form  the  floor  of 
the  mouth  cavity. 

Mucous  Membrane.  —  If,  by  the  aid  of  a  hand  mirror,  one 
looks  within  one's  mouth  cavity,  one  finds  it  lined  with  a  soft, 
moist  covering  of  a  pink  or  red  color.  This  is  called  mu'cous 
membrane.  It  is  much  thinner  than  the  outside  skin,  and 
many  blood  vessels  lie  just  beneath  it.  To  these  facts  is 
due  its  red  color.  Much  of  the  moisture  that  covers  the 
inner  lining  of  the  whole  alimentary  canal  is  the  slimy 
mucus  secreted  by  the  gland  cells  of  the  mucous  membrane. 

2.   THE  TEETH2 

Arrangement  of  the  Teeth.  —  Within  the  mouth  cavity  the 
solid  food  is  cut  into  small 
pieces,  mixed  with  the  juices 
of  the  mouth,  and  then  ground 
into  a  pulpy  mass.  A  large 
part  of  this  work  is  done  by 
the  teeth,  which  are  arranged 
in  two  semicircular  arches. 

They  are  set  in  sockets  formed 

i       ,  P     ,  FIG.  24.  —  Number  and  Positions 

in  the  bone  ot  the  upper  and  of  Teeth  of  Permanent  Set. 

lower  jaws.    The  region  of  the 

jawbones  where  the  teeth  are  imbedded  is  covered  by  the 

gums. 

1  See  "Laboratory  Exercises,"  No.  17. 

2  See  "Laboratory  Exercises,"  No.  17. 


78 


STUDIES  IN  PHYSIOLOGY 


Kinds  of  Teeth.1  —  In  the  complete  set  of  an  adult  there 
are  thirty-two  teeth.  They  may  be  divided  into  four  groups, 
each  kind  of  tooth  having  a  definite  type  of  structure  that 
adapts  it  for  a  special  use.  In  front  there  are  eight  teeth 
with  chisel-shaped  edges.  The  four  upper  teeth  work  upon 
the  corresponding  teeth  of  the  lower  set  something  like  the 
blades  of  a  pair  of  scissors ;  these  eight  teeth  have,  there- 
fore, received  the  name  in-cis'ors  (Latin  inci'sum,  from  inci'do, 
inci'dere  =  to  cut  into).  Just  behind  the  incisors  on  either 
side  of  the  jaw  is  a  tooth  resembling  the  sharp-pointed  teeth 

in  the  mouth  of 

123  4  a  dog ;  from  this 

fact  these  four 
teeth  in  the  hu- 
man mouth  are 
called  canines' 
(Latin  ca'nis  = 
dog).  Still  far- 
ther back  in 
each  half  jaw 
are  two  bi-cus'- 
pids  (Latin  bi  = 
two  4-  cuspis  =  point),  so  called  because  the  free  end  of 
each  has  two  projections,  one  of  which  lies  next  the  cheek, 
the  other  toward  the  interior  of  the  mouth.  (In  other  ani- 
mals, the  teeth  corresponding  to  the  bicuspids  of  man  are 
called  pre-mo'lars.)  The  three  back  teeth  on  either  side  of 
the  upper  and  lower  jaws  have  broad  surfaces,  from  which 
project  four  or  five  elevations.  When  the  food  is  caught 
between  these  mo'lar  teeth  (Latin  molaris  =  a,  millstone),  it 
is  ground  into  a  pulpy  condition,  and  thus  is  well  prepared 
for  mixture  with  the  digestive  juices. 

Dental  Formula.  —  For  convenience  in  comparing  the  teeth 
of  different  animals  we  use  a  form  of  expression  called  a 


FIG.  25.  —  Teeth  from  Half  of  Upper  Jaw. 

1  =  incisors.  2  =  canines. 

3  =  bicuspids  or  premolars.          4  =  molars. 


1  Teeth  of  various  kinds  should  be  procured  from  a  dentist,  and 
should  be  cleaned  by  boiling  in  a  solution  of  caustic  soda. 


A   STUDY   OF   BLOOD   MANUFACTURE  79 

dental  formula.  It  consists  of  a  series  of  fractional  represen- 
tations, the  numerators  of  which  represent  the  teeth  in  the 
upper  jaw,  while  the  denominators  show  the  corresponding 
teeth  of  the  lower  jaw.  The  incisors,  canines,  premolars 
(bicuspids),  and  molars  are  indicated  by  their  initial  letters. 
The  dental  formula  of  man  is,  therefore, 

2  +  2      1  +  1       2+2 


which   means   that  the  adult  human  being  should  have  8 
incisors,  4  canines,  8  bicuspids,  and  12  molars. 

Milk  Teeth.  —  During  early  childhood  there  appears  a  first 
set  of  milk  teeth,  which  later  are  loosened  and  displaced  by 
the  growth  of  the  permanent  set  that  we  have  just  described. 
There  are  but  twenty  teeth  in  the  milk  set,  and  the  formula 
is  as  follows  : 

2  +  2     1  +  1       2  +  2_ 


Bicuspids  are  therefore  wanting,  and  the  milk  molars  occupy 
the  position  in  each  half  jaw  which  later  is  filled  by  the  two 
bicuspids  of  the  permanent  set;  hence,  the  molars  of  the  per- 
manent set  develop  in  a  region  of  the  jaw  that  bears  no  teeth 
during  childhood.  The  teeth  appear  gradually,  the  lower 
incisors  usually  being  the  first  to  push  through  the  gums  at 
about  the  sixth  month.  The  third  permanent  molars  of  each 
half  jaw  often  appear  as  late  as  the  twentieth  year;  they 
are  called  the  wisdom  teeth.1 

Structure  of  Teeth.  —  The  exposed  portion  of  a  tooth  is 
called  its  crown.  It  is  covered  with  a  layer  of  e-nam'el, 
which  is  the  hardest  tissue  in  the  body.  The  root  or  fang  of 

1  The  roots  of  the  milk  teeth  are  gradually  absorbed  and  finally  the 
teeth  loosen  and  come  out.  This  process  is  called  "  shedding"  and  is 
very  slow,  occupying,  in  some  cases,  a  year  or  more.  The  milk  teeth 
are  replaced  by  the  permanent  teeth,  which  appear  usually  after  the 
milk  teeth  are  shed.  The  following  table,  compiled  from  Bromell's 


80 


STUDIES  IN  PHYSIOLOGY 


the  tooth  is  imbedded  in  a  socket  in  the  bone  of  the  jaw. 
It  has  no  enamel,  but  instead  its  outer  layer  is  a  modified 
bone  tissue  called  cement  substance.  The  incisors  and  canines 
usually  have  but  a  single  root ;  the  bicuspids  may  have  two ; 
and  the  molars  are  often  held  in  the  jawbone  by  three, 
four,  or  five  fangs.  In  the  region  between  the  crown  and 
the  fang  is  the  neck  of  the  tooth,  which  is  surrounded  by 
the  gums. 

The  internal  structure  of  a  tooth  is  well  shown  in  a  verti- 
cal section.  The  covering  of  enamel  is  thickest  over  the 
top  of  the  crown ;  it  becomes  thinner  down  the  exposed 
sides,  and  disappears  in  the  neck  region.  The  largest  part 
of  the  tooth  is  composed  of  the  bony  den'tine,  which  consists 
of  fine  processes  extending  from  the  cells  in  the  pulp  cavity 

"  Anatomy  and  Histology  of  the  Mouth  and  Teeth,"  gives  approxi- 
mately the  time  when  these  changes  occur. 


APPEARANCE 

OP 

MILK  TEETH 

BEGINNING 
OF  SHEDDING 
PROCESS 

APPEARANCE 
OF  PERMANENT 
TEETH 

Lower  central  incisors  .... 

6-  8  months 

7th    year 

7-  8  year 

Upper  central  incisors  .... 

6-  8  months 

7th    year 

7-8  year 

Lower  lateral  incisors   .... 

7-  9  months 

8th    year 

8-  9  year 

Upper  lateral  incisors  .... 

7-  9  months 

8th    year 

10-11  year 

Lower  canines  

17-18  months 

12th    year 

12-13  year 

Upper  canines   .... 

17—18  months 

12th    year 

12-13  year 

Lower  1st  deciduous   molar 

(  =  lst  permanent  bicuspid) 

14-15  months 

10th    year 

10-11  year 

Upper  1st  deciduous  molar  .  . 

14-15  months 

10th    year 

10-11  year 

Lower  2d  deciduous  molar  .  . 

18-24  months 

11-12  year 

11-12  year 

Upper  2d  deciduous  molar  .  . 

18-24  months 

11-12  year 

11-12  year 

Lower  1st  permanent  molar  . 

6-  7  year 

Upper  1st  permanent  molar  . 

6-  7  year 

Lower  2d  permanent  molar   . 

12-16  year 

Upper  2d  permanent  molar  . 

12-14  year 

Lower  3d  permanent  molar  . 

Wisdom 

teeth 

16-20  year 

Upper  3d  permanent  molar  . 

Wisdom 

teeth 

17-20  year 

A  STUDY  OF  BLOOD   MANUFACTURE 


81 


and  of  hard  intercellular  substance.  In  the  central  part  of 
the  tooth  is  the  pulp  cavity.  This  region  is  well  supplied 
with  nerves  and  blood  vessels,which  enter  through  a  small 


Cement  or  crusta  petrosa 
Alveolar  periosteum  or  root-membrane 

FIG.  26.  —  Longitudinal  Section       FIG.  27.  — The  Mouth  widely  opened, 
of  a  Canine  Tooth. 

C.p.  =  circumvallate  papillae  of  tongue. 

F.p.  =  fungiform  papillae  of  tongue. 

Tn  =  tonsil. 

Uv  =  uvula  (a  projection  of  the  soft 

palate). 

V=  branches  to  palate  of  fifth  nerve. 
VIII  =  branches  to  tongue  of  ninth  nerve. 

aperture  at  the  end  of  the  fang.  The  blood  furnishes  the 
teeth  with  new  building  material,  and  it  is  probable  that  the 
nerves  in  some  way  direct  the  processes  of  nutrition. 

3.   THE  TONGUE 

Structure  of  the  Tongue.  —  The  tongue  is  an  elongated  mass 
of  muscular  tissue.,  attached  behind  to  the  floor  of  the  mouth. 


82  STUDIES  IN  PHYSIOLOGY 

The  muscle  fibers  run  through  it  in  three  directions,  and  by 
their  separate  or  combined  action  the  free  end  of  this  organ 
can  be  moved  about  at.  will.  When  one  examines  the 
mucous  membrane  on  the  upper  surface  of  the  tongue,  one 
sees  elevations  of  different  sizes,  called  pa-pil'lae  (see  p.  294). 
Nerve  fibers  carry  messages  from  the  papillae  to  the  brain, 
and  thus  we  become  conscious  of  the  senses  of  taste  and 
touch. 

Functions  of  the  Tongue.  —  The  tongue  has  the  following 
uses :  (1)  it  pushes  the  food  between  the  teeth  and  so  helps 
in  the  process  of  mastication ;  (2)  it  is  the  principal  organ 
of  taste ;  (3)  as  soon  as  the  food  is  ready  to  be  swallowed, 
the  tongue  arches  upward  and  forces  the  pasty  mass  back 
into  the  throat ;  (4)  the  tongue  is  likewise  essential  in  speak- 
ing. The  so-called  lingual  (Latin  lingua  =  tongue)  conso- 
nants, t,  d,  and  n,  are  pronounced  when  the  tongue  touches 
the  roof  of  the  mouth. 


4.   THE  SALIVARY  GLANDS 

Position  and  Action  of  the  Salivary  Glands.  —  In  addition  to 
the  mucus  given  out  by  the  mucous  membrane,  the  mouth 
receives  another  secretion  called  sa-li'va.  At  the  sight  or 
smell  of  tempting  food,  "the  mouth  waters."  A  sudden 
fright  or  nervousness,  on  the  other  hand,  stops  the  flow  of 
this  secretion.  Saliva  is  secreted  by  the  salivary  glands. 
Two  of  these  glands,  the  pa-rot'ids  (Greek,  meaning  "beside 
the  ear"),  are  located  near  the  back  part  of  the  lower  jaw- 
bone just  beneath  and  in  front  of  the  ear.  Any  one  who 
has  had  the  mumps  can  readily  locate  these  organs,  for 
mumps  is  a  disease  in  which  the  parotid  glands  swell.  From 
the  parotid  gland  of  each  side  a  duct  conveys  saliva  along 
through  the  walls  of  the  cheek.  This  duct  opens  at  the 
apex  of  a  small  elevation,  easily  felt  with  the  tip  of  one's 
tongue,  on  the  inside  of  the  cheek  opposite  the  upper  second 
molar  teeth  (Fig.  28). 


A  STUDY  OF  BLOOD   MANUFACTURE 


83 


Two  other  pairs  of  glands,  the  sub-max'il-la-ry  (Latin 
sub  =  beneath  +  maxilla  =  jawbone),  and  the  sub-lin'gual 
(Latin  sub  =  beneath  +  lingua  =  tongue),  lie  in  the  muscu- 
lar floor  of  the  mouth  cavity,  and  the  ducts  from  these 
glands  open  in  the  floor  of  the  mouth  under  the  tongue. 

Microscopic  Structure  of  Salivary  Glands. — Each  of  the 
salivary  glands,  when  dissected  and  examined  with  the 
microscope,  reminds  one  of  a 
bunch  of  grapes,  and  for  this 
reason  this  type  of  gland  is 
called  rac'e-mose  (Latin  race- 
mosus  =  full  of  clusters).  The 
principal  duct  of  the  gland 
may  be  compared  to  the  main 
stem  of  the  grape  cluster,  and 
connected  with  this  duct  are 
the  small  ductules  (Latin  duc- 
tus= pipe + ulus = little)  which 
answer  to  the  small  grape 
stems.  At  the  end  of  the 
ductules  are  the  tiny  hollow 
spheres  or  gland  recesses  (re- 
sembling grapes  in  form),  the 
cells  of  which  secrete  the  sa- 
liva. All  parts  of  the  gland 
are  surrounded  and  held  to- 
gether by  fibers  of  connective 

tissue.  Blood  vessels  bring  to  the  gland  cells  the  raw  mate- 
rials from  which  the  saliva  is  produced.  The  workings  of 
the  gland  are  largely  controlled  by  nerve  fibers  that  run 
from  the  brain. 

In  brief,  then,  the  essential  elements  of  the  salivary  glands, 
or  of  any  other  glands,  are  the  special  gland  cells,  the  blood 
vessels,  and  the  nerves. 

Uses  of  Saliva.  —  (1)  The  saliva  aids  the  mucus  in  keeping 
the  mouth  moist,  and  thus  we  are  enabled  to  talk  easily. 


FIG.  28.  —  Dissection  to  show  the 
Salivary  Glands. 

a  =  sublingual  gland. 
b  =  submaxillary  gland, 
c  =  parotid  gland. 
d  =  ducts  from  sublingual  and  sub- 
maxillary  glands. 
e  =  duct  from  parotid  gland. 


84  STUDIES  IN  PHYSIOLOGY 

(2)  It  moistens  the  food  for  swallowing.  The  importance 
of  this  function  is  appreciated  when  one  tries  to  hurry  in 
swallowing  the  crumbs  of  dry  cracker.  (3)  Saliva  dissolves 
sugar  and  salt.  If  the  tongue  is  wiped  dry  and  a  piece  of 
sugar  is  placed  upon  it,  we  have  no  sensation  of  taste  until 
the  sugar  has  been  partially  dissolved  by  the  mixture  of 
saliva  and  mucus  which  are  poured  upon  it.  (4)  Besides 
the  three  mechanical  functions  of  saliva  that  we  have  just 
enumerated,  this  secretion  has  a  chemical  action  upon  cooked 
starch.1  After  a  bit  of  tasteless  starch  paste  has  remained 
on  the  tongue  for  a  short  time,  we  notice  that  it  becomes 
sweet.  This  means  that  the  starch  has  been  changed  to 
grape  sugar  by  the  saliva.  Following  is  a  still  better 
method  of  demonstrating  the  character  of  this  change. 
Put  a  bit  of  the  starch  paste  into  a  test  tube  and  mix 
with  it  some  saliva  from  the  mouth.  After  warming  the 
mixture,  pour  in  some  Fehling's  solution  and  boil.  The 
deep  orange  or  red  color  clearly  demonstrates  the  presence 
of  grape  sugar.  Since  neither  starch  nor  saliva  gives  the 
slightest  test  with  the  Fehling's  solution,  the  grape  sugar 
must  have  resulted  from  the  chemical  action  of  the  saliva 
on  the  starch.  The  principal  ingredients  of  saliva  are 
water  (constituting  over  99%  of  its  composition),  and  a 
kind  of  digestive  ferment  called  pty'arlm  (Greek  ptyalon  — 
spittle).  It  is  the  ptyalin  that  changes  the  starch  to  grape 
sugar. 

5.   THE  THROAT  CAVITY 

The  Uvula. — The  mouth  cavity  communicates  with  the 
throat  by  a  somewhat  narrow  opening.  If  one  holds  a  mir- 
ror in  front  of  the  mouth  opening  and  presses  down  upon 
the  tongue  with  a  spoon,  one  sees  hanging  down  a  small 
fingerlike  extension  of  the  soft  palate,  called  the  u'vu-la. 
When  food  is  swallowed,  this  little  tongue  of  the  soft  palate 
is  shoved  backward  into  a  horizontal  position,  where  it 

iSee  "Laboratory  Exercises,"  No.  19. 


A  STUDY   OF   BLOOD   MANUFACTURE 


85 


helps  to  separate  the  lower  part  of  the  throat  cavity  from  the 
upper  parts  that  commu- 
nicate with  the  nose  cavity. 
The  Air  Passages  and  the 
Epiglottis.  —  The  cavity  of 
the  throat  is  more  or  less 
conical  in  shape,  the  apex  of 
the  cone  narrowing  below 
into  the  esophagus.  The 
windpipe  (tra'chea)  lies  in 
front  of  (or  ventral  to)  the 
gullet  and  conducts  the  air 
from  the  throat  cavity  to  the 
lungs.  At  the  top  of  the 
windpipe  is  the  voice  box 
(lar'ynx).  This  is  readily 
felt  on  the  ventral  surface 
of  the  neck  and  is  com- 
monly known  as  "Adam's 
apple."  When  the  food  is 
being  swallowed,  it  is  of 
course  important  that  the 
windpipe  be  closed,  and  this 
is.  accomplished  by  a  little 
trapdoor  called  the  ep-i-glot'- 
tis  (Greek  epi= upon -{-glottis 
=  opening  from  the  throat 
into  the  larynx).  If  one 
puts  one's  finger  on  the 
larynx  region  and  then  swal- 
lows, one  can  feel  this  organ 
rising  to  meet  the  epiglottis. 
Breathing  and  Swallowing. 
—  Thus  far  we  have  de- 
scribed five  openings  con- 
nected with  the  throat  cavity :  two  for  the  food  (one  lead 


FIG.    29.— Longitudinal    Section    of 
Head  and  Neck,  showing  Food  and 
Air  Passages. 
a  =  vertebral  column. 
6  =  esophagus, 
c  =  windpipe. 
d  =  larynx. 
e  =  epiglottis. 
/  =  soft  palate  and  uvula. 
g  =  opening  of  left  Eustachian 

tube. 

h  =  opening  of  left  tear  duct. 
i  =  hyoid  bone. 
k  —  tongue. 
I  =  hard  palate. 
m,  n  =  base  of  skull. 
°>P>Q  =  upper,    middle,    and    lower 
turbinate  bones. 


86  STUDIES  IN  PHYSIOLOGY 

ing  from  the  mouth,  the  other  opening  into  the  gullet), 
and  three  for  the  air  (the  first  two  letting  in  the  air  from 
the  nose,  the  third,  conducting  it  through  the  glottis)  to  the 
lungs.  But  one  set  of  these  openings  can  be  used  at  the 
same  time,  for  one  sees  from  Fig.  29  that  the  paths  of  food 
and  air  cross  each  other  in  the  throat.  Hence,  if  we  try  to 
breathe  and  swallow  at  the  same  instant,  the  food  starts 
"  down  the  wrong  way,"  that  is,  down  the  windpipe. 

The  Eustachian  Tubes. — A  simple  experiment  demon- 
strates the  presence  of  an  additional  pair  of  openings,  con- 
necting the  throat  with  the  ear.  Close  the  mouth,  grasp 
the  nose  firmly  so  as  to  close  its  external  openings,  and  then 
force  air  upwards  several  times  from  the  lungs.  The  crack- 
ling sound  is  due  to  the  momentary  stretching  of  the  ear 
drums  by  the  increased  pressure  of  the  air  on  their  inner 
surface.  The  Eu-sta'chi-an  tubes  (so  named  from  their  dis- 
coverer, a  learned  Italian  physician),  carry  this  air  from  the 
upper  part  of  the  throat  cavity  into  the  middle  region  of 
the  ear.  The  ringing  sensation  in  the  ears  when  one  has  a 
cold  in  the  head  is  due  to  the  temporary  closing  of  these 
tubes. 

The  Process  of  Swallowing.  —  The  food  can  be  kept  in  the 
mouth  as  long  as  we  wish,  but  when  once  it  has  been  pushed 
back  into  the  throat  it  is  beyond  our  control.  The  uvula 
blocks  the  way  toward  the  nose  cavity,  the  windpipe  is 
closed  by  the  epiglottis,  and  the  muscles  that  surround  the 
throat  cavity  quickly  close  in  about  the  food  and  force  it 
down  the  gullet.  This  rapid  clearing  of  the  throat  is  nec- 
essary in  order  that  breathing  may  be  resumed.  As  soon 
as  the  food  reaches  the  gullet,  the  windpipe  is  opened  by  the 
lowering  of  the  larynx  and  by  the  elevation  of  the  epiglot- 
tis, and  at  the  same  time  the  soft  palate  drops  down  into  a 
vertical  position,  thus  opening  the  passages  from  the  nose. 
Hence,  when  food  particles  start  down  the  windpipe  and 
we  cough,  the  food  is  often  forced  out  through  the  nose, 
since  this  is  the  only  passage  way  that  is  clear  (see  Fig.  29). 


A   STUDY   OF  BLOOD   MANUFACTURE 


87 


6.   THE  ESOPHAGUS 

Structure  of  the  Esophagus. — The  esophagus  traverses  the 
length  of  the  chest  cavity,  and  as  it  nears  the  stomach  it 
goes  through  the  diaphragm.  In  a  cross  section  of  this  tube 
the  following  tissues  appear.  Like  all  other  parts  of  the 
alimentary  canal,  it  is  lined  with  mucous  membrane,  which 
furnishes  a  soft, 
moist  surface  for 
the  passage  of  food. 
Outside  the  mu- 
cous membrane  are 
rings  of  circular 
muscle  running 
around  the  esopha- 
gus, and  a  longi- 
tudinal layer  of 
muscle  is  found 
outside  the  circu- 
lar muscles. 

Functions  of  the 
Esophagus.  —  The 
food  is  pushed 
slowly  down  this  «  =  esophagus. 

6  =  cardiac  region  of  stomach. 

c  =  upper  wall  of  stomach. 

d  =  pyloric  region  of  stomach. 

e  —  bile  duct  from  liver. 

/=  gall  bladder. 

g  =  duct  from  pancreas. 
h,  i  =  small  intestine  showing  ridges. 


FIG.  30.  —  Longitudinal  Section  of  Stomach  and 
Small  Intestine. 


straight  tube  by  the 
successive  contrac- 
tion of  the  rings 
of  muscle  described 
above.  Swallowing 
is,  therefore,  not  a 
mere  dropping  of  the  food  into  the  stomach,  for  the  walls  of 
the  esophagus  are  pressed  together  by  surrounding  organs, 
except  when  the  tube  is  opened  by  the  passing  food.  In 
fact,  after  practice  one  can  swallow  when  standing  on  one's 
head,  and  most  quadrupeds  (horse,  dog,  cow)  when  feeding 
hold  the  head  below  the  level  of  the  stomach. 


88 


STUDIES  IN  PHYSIOLOG1 


7.   THE  STOMACH 

Position,  Size,  Shape.  —  The  stomach  lies  about  midway 
between  the  upper  and  lower  ends  of  the  trunk,  with  its 
larger  end  lying  toward  the  left  side  of  the  body.  It  is  a 

muscular  pouch,  shaped  more 
or  less  like  a  pear  or  a  crook- 
neck  squash.  When  moder- 
ately filled,  it  holds  about 
three  pints.  The  esophagus 
communicates  with  the  upper 
region  of  the  larger  end  of 
the  stomach,  and  since  this 
opening  into  the  stomach  is 
near  the  apex  'of  the  heart, 
c  it  has  received  the  name  car'- 
di-ac  orifice  (Greek  Tcardia  = 
heart).  The  small  intestine 
is  continuous  with  the  right 
end  of  this  organ,  the  com- 
munication between  the  two 
the  py-lo*rus  (from  Greek, 
gate  keeper)  being 
by  a  ring  of  muscle 
'ic  sphinc'ter 


FIG.   31.  -Three    Gastric    Glands 
(Cardiac  Portion  of  Stomach). 


=  connective     tissue      between    called    the 


(from  Greek,  meaning  to  bind 
tight)  (see  Pig.  30). 

The  Mucous  Lining  and  Gastric 
Glands.  — When  the  stomach  is 
full  of  food,  the  lining  pre- 
sents a  smooth  surface.  This 

becomes  folded  into  ridges  as  the  food  is  forced  outward 
into  the  intestines.  The  important  glands  of  the  stomach 
are  those  which  secrete  the  gas'tric  juice.  This  digestive  fluid 
is  composed  of  water  (over  99%),  free  hy-dro-chlo'ric  acid, 


glands. 

e  =  cells  lining  the  stomach, 
ra  =  mouth  of  gland. 
ov  =  ovoid  cells    (possibly  secrete 

hydrochloric  acid). 
p  =  cylindrical  cells  (probably  se- 
crete pepsin) . 


A   STUDY   OF  BLOOD   MANUFACTURE 


89 


and  a  digestive  ferment  called  pep  'sin.1  If  one  examines  with 
a  magnifying  lens  the  mucous  lining  of  the  stomach,  one  sees 
a  countless  number  of  small  orifices  that  look  like  pinholes. 
These  are  the  pores  through  which  gastric  juice  is  dis- 
charged from  the  gas'tric  glands.  The  microscopic  structure 
of  one  of  these  glands  is  best  studied  in  a  thin  section  cut 
at  right  angles  to  the  surface  through  the  wall  near  the  car- 
diac end  of  the  stomach.  The  surface  pore  is  the  opening 
from  a  compara- 
tively short  duct, 
and  connected  with 
this  are  two  or 
three  tiny  finger- 
shaped  recesses, 
each  one  of  which 
is  lined  with  a 
single  layer  of  cy- 
lindrical cells  (Fig. 
31).  Outside  this 
layer  are  other  egg- 
shaped  cells,  which 
give  to  the  gas- 
tric glands  their 
peculiar  beaded  ap- 
pearance. It  is 
probable  that  the 
pepsin  of  the  gastric  juice  is  secreted  by  the  cylindrical  cells. 
It  is  then  discharged  through  the  ducts  when  the  food  enters 
the  stomach.  The  origin  of  the  hydrochloric  acid  has  never 
been  satisfactorily  explained;  some  physiologists  believe, how- 
ever, that  it  comes  from  the  egg-shaped  cells  mentioned  above. 
Blood  Supply  of  the  Stomach.  —  Beneath  the  mucous  lining 
of  the  stomach  is  a  rich  supply  of  blood  vessels.  The  blood 
brings  to  the  stomach  the  chemical  compounds  necessary  for 

1  In  the  gastric  juice  is  also  found  another  ferment  called  ren'nin, 
which  coagulates  milk. 


Mucous  lining 

containing 

glands. 


Submucous 
layer  contain- 
ing blood  ves- 
sels and  con- 
nective tissue. 


Circular,  ob- 
lique, and 
1  i  gitudinal 
muscles. 

Outer  covering 
of  connective 
tissue. 


FIG.  32.  —  Section  of  Wall  of  Stomach. 

Magnified  twelve  times.    Photographed  through 
the  microscope. 


90  STUDIES  IN  PHYSIOLOGY 

the  secretion  of  gastric  juice,  supplies  the  building  materials 
required  for  the  growth  and  repair  of  the  muscles,  and,  as 
we  shall  see  later,  carries  away  from  this  organ  whatever 
digested  food  it  can  absorb. 

Muscles  of  the  Stomach.  —  The  chief  function  of  the  human 
stomach  is  to  secrete  the  gastric  juice  and  to  mix  thoroughly 
this  juice  with  the  food.  The  muscular  walls  are  admirably 
adapted  to  this  purpose.  On  stripping  off  the  outer  cover- 
ing of  connective  tissue,  one  finds  layers  of  longitudinal, 
circular,  and  oblique  muscles  that  constitute  the  larger  por- 
tion of  the  thickness  of  the  stomach  wall  (Fig.  32).  Cir- 
cular fibers  form  the  strong  ring  of  muscle  (pyloric  sphincter) 
that  closes  the  pyloric  end  of  the  stomach  from  the  small 
intestine  (Fig.  31,  d). 

When  the  food  reaches  the  stomach,  the  gastric  juice 
oozes  out  upon  it,  and  the  mixture  is  pushed  back  and  forth 
and  up  and  down  by  the  successive  action  of  the  different 
sets  of  muscles.  The  return  of  the  food  to  the  mouth  cavity 
is  prevented  by  the  contraction  of  the  circular  muscles  at 
the  cardiac  orifice,  except  in  case  of  nausea,  when  they 
relax  and  allow  the  stomach  to  rid  itself  of  its  contents. 
The  pyloric  sphincter  relaxes  from  time  to  time,  and  the 
food  that  has  been  sufficiently  digested  is  pushed  on  into  the 
intestine.  Fortunately  for  the  well-being  of  the  body,  all 
these  processes  are  entirely  automatic,  that  is,  they  are 
carried  on  without  our  conscious  direction.  The  muscles 
of  the  alimentary  canal  for  this  reason  are  called  in-voVun- 
ta-ry  (Latin  in  =  without  -f  voluntas  =  will).  Their  activ- 
ity is  largely  controlled  by  the  syni-pa-thet'ic  nervous  system, 
which  will  be  described  later. 

Digestion  in  the  Stomach.1  —  The  gastric  juice  has  no  effect 
whatever  on  the  nutrients  starch  and  fats.  Sugars  and 
soluble  salts  (that  is  salts  that  dissolve  in  water),  if  not 
dissolved  in  the  mouth,  are  readily  liquefied  by  the  water  of 
the  gastric  juice. 

i  See  "Laboratory  Exercises,"  No.  20. 


A  STUDY  OF  BLOOD  MANUFACTURE  91 

Certain  mineral  food  substances,  however,  like  phosphate 
of  lime  found  in  milk,  are  not  soluble  in  water,  and  these 
insoluble  salts  reach  the  stomach  unchanged.  The  hydro- 
chloric acid  of  the  gastric  juice  soon  converts  them  into 
soluble  salts,  which  are  then  dissolved.  Thq,  following  ex- 
periment will  illustrate  this  process.  Put  a  little  of  the 
phosphate  of  lime  into  a  test  tube,  add  water,  and  shake. 
The  mixture  assumes  a  milky  appearance,  and  after  a  time 
the  phosphate  of  lime  settles  to  the  bottom,  showing  that 
this  kind  of  mineral  matter  will  not  dissolve  in  water.  The 
addition  of  a  small  amount  of  hydrochloric  acid  immediately 
clears  the  mixture,  for  the  phosphate  of  lime  is  converted 
into  chloride  of  lime,  which  is  a  soluble  salt. 

Digestion  of  Proteids.1  —  The  most  important  function  of 
the  stomach  is  its  digestive  action  on  proteids.  The  white 
of  egg,  lean  meat,  or  the  gluten  of  wheat  reaches  the  stomach 
in  a  pulpy  mass,  and  this  is  insoluble  in  water.  The  casein 
of  milk,  which  is  a  liquid  when  swallowed,  becomes  curdled 
by  the  action  of  the  hydrochloric  acid.  Before  these  most 
important  proteids  can  be  absorbed  to  become  a  part  of  the 
blood,  they  must  be  chemically  changed  into  a  kind  of 
soluble  proteid  called  pep'tone.  The  principles  of  proteid 
digestion  can  be  illustrated  in  the  following  way :  Cut  into 
fine  bits  a  piece  of  hard-boiled  egg,  and  divide  the  minced  egg 
into  four  portions.  Put  one  fourth  into  a  test  tube  (No.  1) 
and  add  water.  Into  another  test  tube  (No.  2)  put  a  second 
portion  of  minced  egg,  water,  and  a  little  hydrochloric  acid. 
To  a  third  portion  (test  tube  No.  3)  add  water  and  a  little 
pepsin.  (Pepsin  readily  dissolves  in  water.)  The  rest  of 
the  egg  in  test  tube  No.  4  should  be  treated  with  all  the  in- 
gredients of  gastric  juice  (water,  pepsin,  and  hydrochloric 
acid).  Since  the  food  in  the  stomach  is  in  constant  motion, 
and  since  the  temperature  within  the  body  (98 i°  F.)  is 
considerably  higher  than  that  of  the  surrounding  air,  these 
conditions  should  be  imitated  so  far  as  possible  by  frequently 
1  See  "Laboratory  Exercises,"  No.  21. 


92  STUDIES   IN  PHYSIOLOGY 

shaking  the  tubes  and  by  leaving  them  in  a  warm  place. 
At  the  end  of  several  hours,  the  egg  in  test  tube  No.  4, 
which  was  treated  with  all  the  ingredients  of  gastric  juice, 
is  found  to  be  dissolved,  but  the  pieces  remain  practically 
unchanged  in  ^Jie  other  tubes.  We  infer  therefore  that  the 
proteid  of  egg  is  digested  by  the  combined  action  of  pepsin, 
hydrochloric  acid,  and  water. 

An  instructive  experiment  may  be  performed  in  a  fifth 
test  tube  by  adding  the  three  ingredients  of  gastric  juice  to 
a  large  piece  of  egg.  It  will  be  found  that  a  much  longer 
time  is  required  to  digest  the  egg  in  this  condition.  Hence, 
we  see  that  if  food  is  not  properly  chewed,  the  stomach  is 
compelled  to  ck)  a  considerable  amount  of  extra  work. 

One  might  ask  the  interesting  question,  Why  does  not 
the  stomach  digest  itself  ?  When  we  eat  a  piece  of  tripe, 
which  is  prepared  from  the  walls  of  a  cow's  stomach,  the 
tripe  is  liquefied  by  our  gastric  juice.  Why,  then,  does  not 
our  gastric  juice  dissolve  the  walls  of  our  stomach?  All 
we  know  is  that  in  some  unknown  way  our  stomach  tissues 
when  alive  are  able  to  resist  this  solvent  action. 

8.   THE  SMALL  INTESTINE 

Position  and  Size.  —  The  small  intestine  is  a  much  coiled 
tube,  filling  the  larger  portion  of  the  abdominal  cavity  (see 
Fig.  23).  It  is  usually  twenty  feet  or  more  in  length,  and 
therefore  constitutes  nearly  four  fifths  of  the  whole  length 
of  the  alimentary  canal.  Beginning  at  the  pyloric  end  of  the 
stomach  with  a  diameter  of  about  two  inche^  it  decreases 
somewhat  in  size  until  it  opens  into  the  large  intestine. 

Peritoneum.  —  The  whole  abdominal  cavity  is  lined  with 
a  thin,  smooth  membrane  called  per-i-to-ne'um  (Greek  peri 
=  around  -f-  teinein  =  to  extend).  Sheets  of  peritoneum  like- 
wise inclose  the  various  organs  found  in  the  abdominal 
cavity,  and  connect  these  organs  with  the  wall  of  the  ab- 
domen. Per-i-to-ni'tis  is  an  inflammation  of  any  portion  of 
this  membrane.  To  the  thin  sheets  of  connective  tissue  and 


A  STUDY   OF  BLOOD   MANUFACTURE  93 

peritoneum  that  hold  the  small  intestine,  in  place  is  given 
the  name  mes'en-ter-y  (see  Fig.  33). 

Functions  of  the  Small  Intestine.  —  In  order  to  understand 
the  structure  of  this  part  of  our  digestive  organs,  we  must 
bear  in  mind  that  one  of  its  principal  functions  is  to  soak  up  or 
absorb  digested  food.  To  accomplish  this,  the  food  must  be 
moved  along  slowly  close  to  the  minute  blood  vessels  and 
other  tubes  which  are  to  carry  off  to  other  parts  of  the  body 


FIG.  33.  —  Diagram  of  Cross  Section  of  Abdomen.     (In  reality  the  larger 
part  of  the  abdominal  cavity  is  filled  with  the  coils  of  the  intestine.) 

b.v  =  blood  vessels.  d.m  =  muscles  of  the  back. 

m1,  m2,  m8  =  three  muscle  layers  of  abdominal  wall.         rues  =  mesentery. 
perit  =  peritoneum.  sk  =  skin.  vert  =  vertebra. 

the  liquefied  nutrients.     We  shall  soon  see  the  wonderful 
adaptations  of  the  intestine  for  this  purpose. 

In  the  intestines,  too,  important  digestive  processes  are 
carried  on  by  the  juices  that  come  from  the  liver  and  pan- 
creas. The  chemical  changes  in  the  food  brought  about  by 
pancreatic  juice  and  bile  will  be  discussed  in  connection 
with  the  organs  by  which  these  digestive  fluids  are  secreted. 
Beneath  the  peritoneum  are  layers  of  circular  and  longitu- 
dinal muscle.  By  their  rhythmical  contraction  the  food  is 


94  STUDIES  IN  PHYSIOLOGY 

slowly  forced  on  toward  the  large  intestine.     This  succession 
of  contractions  and  relaxations  is  called  per-i-stal 'sis. 

Adaptations  for  Absorption.  —  In  the  small  intestine  the 
mucous  membrane  is  developed  to  an  extraordinary  degree. 
In  the  first  place  this  lining  is  elevated  into  ridges  that  run 
two  thirds  of  the  way  around  the  interior  wall  and  some  of 
them  project  about  a  third  of  an  inch  into  the  cavity  of  the 


FIG.  34.  —  Cross  Section  of  Intestine  of  a  Mouse.   (Ridges  are  not  present.) 

Magnified  fifteen  times.  Photographed  through  the  microscope.  A  large 
number  of  villi  project  toward  the  interior  of  the  intestines.  The  dark 
lines  show  the  blood  vessels  filled  with  a  colored  mixture. 

intestines.  These  crescent-shaped  ridges  are  most  numer- 
ous near  the  stomach  and  gradually  disappear  in  the  region 
near  the  large  intestine  (Fig.  30).  Like  little  dams,  they 
delay  the  onward  flow  of  the  food,  and  they  also  increase 
considerably  the  surface  for  absorption.  The  absorbing 
surface  is  multiplied  still  further  by  the  vil'li. 

The  Villi.  —  If  one  puts  into  water  a  piece  of  the  small 
intestine  of  a  sheep,  and  examines  with  a  hand  lens  the 
mucous  lining,  one  sees  that  the  ridges  and  depressions  are 


A   STUDY  OF   BLOOD   MANUFACTURE 


95 


covered  with  tiny  hairlike  processes  that  give  a  velvety 
appearance  to  the  surface.  Each  of  these  minute  elevations 
is  called  a  vil'lus  (Latin  vittus  =  a  tuft  of  hair).  The  villi  are 
exceedingly  numerous  in  the  small  intestine  of  man,  the  total 
number  being  estimated  at  about  four  millions. 

Each  villus,  when  highly  magnified,  is  found  to  be  a  com- 
plicated structure.  Up  through  its  center  pass  one  or  more 
hollow  tubes,  the  closed  ends 
of  which  lie  just  beneath  the 
cells  that  cover  the  top  of 
the  villus.  The  tubes  of  the 
different  villi  connect  with 
one  another  and  are  of  great 
importance  in  carrying  away 
from  the  intestine  the  fats 
that  are  absorbed.  If  a  cat 
is  fed  with  milk  and  after 
three  or  four  hours  is  killed, 
one  can  see  that  these  minute 
vessels  in  the  villi  and  the 
larger  tubes  in  the  mesentery 
into  which  they  empty  are 
filled  with  a  milky  stream  of 
the  absorbed  fat  droplets. 
For  this  reason  the  tubes  are 
called  lac'teals  (Latin  lac, 
foc&'s  =  milk). 

Around  the  lacteal  of  each 
villus  is  a  network  of  minute 
blood  vessels.  Since  they  lie  close  to  the  single  layer  of 
cylindrical  cells  which  cover  the  outer  surface  of  the  villus, 
the  liquefied  food  is  readily  absorbed  by  the  blood  current. 
One  may  therefore  compare  the  absorbent  action  of  the  villi 
with  the  absorption  that  takes  place  through  the  walls  of  the 
root  hairs  of  plants.  In  structure,  however,  a  villus  is  very 
much  more  complicated  than  is  a  root  hair. 


FIG. 


35.  — Diagram  of  Two   Villi, 
highly  magnified. 

b.v  =  blood  vessels. 
e  =  cells  covering  villi. 
I  =  lacteals  for  absorbing  fat. 


96  STUDIES  IN  PHYSIOLOGY 

9.   THE  LARGE  INTESTINE 

Position,  Form,  Size. — The  large  intestine  is  the  last  por- 
tion of  the  alimentary  canal.  It  is  a  tube  'five  or  six  feet 
long,  with  a  diameter  gradually  decreasing  from  two  and 
a  half  or  three  inches  to  an  inch  at  its  lower  end.  Beginning 
in  the  lower  right-hand  region  of  the  abdominal  cavity  as  a 
saclike  pouch  called  the  cm' cum  (Latin  caecum  =  blind  sac) 
(Fig.  23),  the  large  intestine  passes  anteriorly  on  the  right 
side  (the  ascending  colon)  to  the  lower  surface  of  the  stom- 
ach ;  it  then  crosses  the  abdominal  cavity  (transverse  colon) ; 
a  third  portion  (the  descending  colon)  runs  posteriorly  on 
the  left  side.  The  large  intestine  then  takes  an  S-shaped 
course  (sigmoid  flexure)  and  passes  to  the  exterior  of  the 
body  by  a  short,  straight  tube,  the  rectum  (Latin  rectus  = 
straight). 

Ileo-caecal  Valve.  — The  final  portion  of  the  small  intestine 
(called  the  il'e-um)  opens  into  the  side  of  the  large  intestine 
in  the  region  of  the  caecum  by  a  so-called  il-eo-cce'cal  orifice. 
This  is  guarded  by  two  flaps  of  membrane.  The  food  can 
pass  into  the  large  intestine,  but  its  return  to  the  small  in- 
testine is  prevented  by  this  double-flapped  ileo-ccecal  valve, 
which  works  on  the  same  principle  as  the  valve  in  a  bicycle 
tire;  after  air  has  been  forced  into  the  tire,  the  valve 
immediately  closes  to  prevent  its  escape. 

Vermiform  Appendix.  —  Connected  with  the  caecum  is  a 
small  tubelike  sac  about  the  size  of  a  pencil,  and  usually 
about  four  inches  long  (Fig.  23).  From  its  more  or  less 
twisted  shape  it  has  received  the  name  ver'mi-form  ap-pen'dix 
(Latin  vermiform  =  worm-shaped).  The  appendix  of  rab- 
bits (see  Fig.  4,  P)  and  of  several  other  herbivorous  animals 
is  of  considerable  use  in  the  process  of  absorption.  In  man, 
however,  it  has  lost  this  importance,  and  remains  as  a  small 
and  probably  useless  extension  of  the  caecum.  Ap-pend-i- 
ci'tis  is  a  diseased  condition  arising  from  inflammation  in 
the  tissues  of  the  appendix.. 


A  STUDY  OF  BLOOD  MANUFACTURE  97 

10.   THE  PANCREAS 

Position,  Form,  Size.  —  One  of  the  most  important  of  the 
digestive  glands  is  the  pan'cre-as,  which  is  situated  just 
below  the  stomach.  In  shape  this  organ  may  be  compared 
with  that  of  a  dog's  tongue.  It  extends  horizontally  from 
a  curve  of  the  small  intestine  near  the  pylorus  to  the  spleen 
at  the  left  side  of  the  body  (Fig.  23).  The  pancreas  is  usu- 
ally a  little  over  six  inches  in  length. 

Structure  of  the  Pancreas.  —  Like  the  salivary  glands,  the 
pancreas  is  a  racemose  gland,  consisting  of  gland  recesses, 
ductules,  and  a  main  duct.  The  latter  extends  through  the 
length  of  the  pancreas,  and  after  uniting  with  a  duct  from 
the  liver  (Fig.  30,  g),  opens  into  the  small  intestine  not  far 
from  the  pylorus.  Within  the  gland  recesses  is  secreted  the 
pancreatic  juice,  which  is  poured  out  through  the  duct  just 
described  upon  the  food  after  it  has  entered  the  small  intestine. 

Functions  of  the  Pancreatic  Juice.  —  The  pancreatic  juice  is 
alkaline.  The  food  mass,  therefore,  becomes  alkaline  soon 
after  it  enters  the  intestine.  Pancreatic  juice  digests  three 
of  the  nutrients,  namely,  starch,  proteids,  and  fats.  Indeed, 
with  the  single  exception  of  insoluble  salts,  our  foods  could 
be  digested  by  this  one  juice.  Like  saliva,  pancreatic  juice 
changes  starch  into  sugar,  and  like  gastric  juice,  it  converts 
proteids  into  peptones.  The  pepsin  of  the  gastric  juice, 
however,  always  requires  the  presence  of  an  acid  (hydro- 
chloric), while  the  ferments  of  the  pancreatic  juice  work 
only  in  the  presence  of  an  alkali. 

Digestion  of  Fats.1  —  The  heat  of  the  body  melts  much  of 
the  fat  before  it  reaches  the  intestine,  but  this  liquid  cannot 
be  absorbed  until  it  has  been  digested  more  thoroughly. 
Pancreatic  juice  digests  fats  in  two  ways  :  either  by  making 
them  into  an  e-mul'sion,  or  by  converting  them  into  soap  and 
glycerin.  The  latter  process  is  called  sa-pon-i-Ji-ca'tion  (Latin 
sapo  =  soap  -\-facere  =  to  make).  These  changes  are  shown 
1  See  "Laboratory  Exercises,"  No.  22. 

H 


98  STUDIES   IN  PHYSIOLOGY 

in  the  following  experiments :  Put  into  a  test  tube  a  small 
amount  of  olive  oil  or  melted  butter,  add  water  and  shake. 
The  oil  is  broken  up  into  small  spheres  and  mingled  with 
the  water  during  the  process  of  shaking.  When  the  test 
tube  is  set  aside,  however,  the  oil  rises  to  the  surface,  show- 
ing that  the  two  liquids  will  not  remain  combined. 

If,  now,  a  solution  of  caustic,  soda  or  other  alkali  be 
shaken  up  with  the  oil  and  water,  the  mixture  assumes  a 
milky  appearance,  and  the  oil  does  not  then  rise  to  the  top 
in  a  clear  layer  as  it  did  after  being  shaken  with  the  water. 
Fat,  when  thus  mixed  with  an  alkali,  forms  an  emulsion. 
If  a  drop  of  this  mixture  is  examined  with  a  compound 
microscope,  tiny  spheres  of  fat  are  seen  floating  about  in  a 
colorless  liquid.  Each  little  sphere  is  inclosed  by  a  thin 
covering  of  the  alkali,  and  thus  the  fat  droplets  are  kept 
separate  from  each  other.  Water  will  not  form  this  thin 
covering,  nor  will  an  acid.  For  this  reason,  fats  are  not 
emulsified  in  the  stomach.  They  are  acted  upon  only  by 
the  strongly  alkaline  juices  of  the  intestine.  A  still  better 
emulsion  can  be  formed  by  shaking  the  oil  with  raw  white 
of  egg.  In  this  case  the  fat  globules  are  surrounded  by  a 
thin  layer  of  albumin.  Milk  is  an  emulsion  consisting 
of  fat  (cream)  and  of  liquid  proteids. 

When  the  emulsion,  made  by  mixing  the  oil  and  the  alkali, 
is  heated,  a  chemical  change  takes  place  and  some  of  the 
fat  is  converted  into  soap  and  glycerin.  Both  of  the  latter 
are  readily  soluble  in  water,  and  so  can  be  easily  taken  up 
by  the  blood.  The  pancreatic  juice  acts  upon  fats  in  both 
the  ways  we  have  been  describing.  Since  it  is  alkaline,  it 
forms  an  emulsion.  It  can  likewise  change  fats  into  soap 
and  glycerin.  When  these  compounds  get  into  the  blood, 
however,  they  are  changed  again  into  fats. 

11.   THE  LIVER 

Position,  Form,  Size The  human  liver  is  the  largest  gland 

of  the  body,  weighing  three  to  four  pounds.      It  lies  toward 


A  STUDY   OF  BLOOD  MANUFACTURE 


99 


the  right  side  of  the  body,  just  beneath  the  diaphragm,  and 
partially  covers  the  py- 
loric  end  of  the  stomach. 
It  consists  of  several 
lobes,  and  on  its  under 
surface  is  a  small,  green- 
ish brown  sac  called  the 
gall  bladder.  The  deep 
red  color  of  the  liver  is 
partly  due  to  the  fact 
that  one  fourth  of  all 
the  blood  of  the  body  is 
found  within  its  tissues. 
Functions  of  the  Liver. 
—  The  liver  performs 
three  important  func- 
tions. In  the  first  place, 
it  secretes  a  golden 
brown  liquid  called  the 
bile,  which  is  either 
poured  at  once  through 
the  bile  duct  into  the 
small  intestine  or  is 
stored  in  the  gall  blad- 
der until  needed.  If 
the  bile  duct  becomes 
stopped  up,  the  bile  is 
absorbed  into  the  blood 
and  gives  to  the  tissues 
the  yellow  tint  that  is 
characteristic  of  jaun- 
dice. The  liver,  in  the 


second  place,  serves  as  a 
great  storehouse  for  the 
carbohydrates  when  the 
blood  does  not  need  them  for  immediate  use. 


FIG.  36.  — The  Organs  of  the  Abdomen. 

ac  =  ascending  colon   (cut  off  at 
top). 

ad  =  descending  colon  (cut  off  at 

top). 

a,  b,  c,d,e  =  portal  vein  and  its  branches 
which  carries  blood  to  liver 
from  stomach,  spleen,  pan- 
creas, and  intestines. 

du  =  part  of  small  intestine  (cut 
off). 

gT)  =  gall  bladder. 

.  h  =  ducts  from  gall  bladder  and 

liver. 

I  =  under  surface  of  liver. 
p  =  pancreas. 

sp  =  spleen. 

st  =  stomach. 


We  shall  see 


100  STUDIES  IN  PHYSIOLOGY 

in  a  later  chapter  that  all  the  blood  from  the  stomach  and 
intestines  passes  through  the  liver  on  its  way  back  to  the 
heart.  If  this  blood  contains  more  sugar  than  is  needed, 
the  excess  is  left  behind  in  the  liver  cells,  where  it  is 
changed  to  a  kind  of  animal  starch  called  gly'co-gen.  When, 
on  the  other  hand,  there  is  a  lack  of  carbohydrates  in  the 
blood,  some  of  the  supply  in  the  liver  is  changed  back  to 
sugar  and  is  taken  up  again  by  the  blood.  Finally,  the 
liver  helps  to  destroy  some  of  the  worn-out  cells  of  the 
blood  (the  red  corpuscles),  and  the  waste  materials  thus 
formed  are  passed  off  into  the  intestine  as  a  part  of  the  bile. 

Functions  of  the  Bile.  —  We  have  already  noted  the  fact 
that  the  bile  duct  and  the  duct  from  the  pancreas  unite 
before  reaching  the  intestine.  Hence,  the  bile  and  pancreatic 
juice  are  mixed  when  they  are  poured  upon  the  food.  It  is 
difficult,  for  this  reason,  to  distinguish  with  certainty  between 
the  functions  of  the  two  juices.  Some  physiologists  main- 
tain that  the  bile  forms  an  emulsion  with  fats  after  the 
same  manner  as  the  pancreatic  juice;  others  declare  that  it 
has  no  digestive  action  whatever,  and  is  merely  a  waste  ma- 
terial passed  off  by  the  liver  into  the  intestine. 

We  know  that  the  bile  is  alkaline;  it  is  therefore  probable 
that  at  least  it  assists  the  pancreatic  juice  in  digesting  fats. 
It  is  certainly  true  that  the  absorption  of  fats  through  the  cells 
of  the  villi  into  the  lacteals  is  promoted  by  the  presence  of 
bile,  for  in  cases  of  jaundice  a  considerable  percentage  of  the 
fats  we  eat  is  discharged  from  the  large  intestine  with  the 
waste  material.  Again,  the  alkaline  bile  causes  the  muscles 
of  the  intestines  to  contract  rhythmically,  thus  forcing  the 
food  onward  toward  the  large  intestine.  For  this  reason,  the 
best  means  of  avoiding  constipation  is  to  secure  the  presence 
of  a  sufficient  quantity  of  bile  in  the  intestine.  Calomel 
and  similar  drugs  are  often  given  in  case  of  constipation, 
because  they  stimulate  the  liver  to  greater  activity.  And, 
finally,  bile  acts  as  an  antiseptic  to  prevent  the  decay  of  the 
refuse  material  as  long  as  it  remains  within  the  intestines. 


A  STUDY  OF  BLOOD 


12.   ABSORPTION  FROM  THE  ALIMENTARY  CANAL 

Necessity  for  Absorption.  —  We  have  now  learned  some- 
thing of  the  processes  of  digestion.  We  have  seen  that  the 
foods  we  eat  are  ground  up  in  the  mouth  cavity  by  the  teeth, 
and  thus  made  ready  for  the  action  of  the  various  digestive 
juices.  We  have  also  demonstrated  that  sugars  and  soluble 
salts  are  dissolved  in  the  mouth  ;  that  insoluble  mineral 
matters  are  made  soluble  in  the  stomach;  that  starch  is 
changed  to  sugar  by  the  saliva  and  pancreatic  juice  ;  that 
proteids  are  converted  into  peptones  by  the  pancreatic  and 
gastric  juices  ;  and  that  fats  are  emulsified  or  saponified 
in  the  intestines  by  the  combined  action  of  bile  and  pan- 
creatic juice.  Were  the  food  to  remain  within  the  alimentary 
canal,  however,  even  though  it  had  been  thoroughly  digested, 
it  would  still  be,  in  a  certain  sense,  outside  the  body,  since 
this  canal  is  a  continuous  tube  opening  to  the  exterior  at 
either  end.  In  order  to  furnish  material  for  building  and 
repairing  the  various  tissues,  the  liquid  nutrients  must  be 
distributed  to  the  tissues,  wherever  needed.  This  is  accom- 
plished through  the  agency  of  the  blood  system.  We  have 
now  to  consider  the  process  of  absorption,  which  includes  the 
final  steps  whereby  foods  become  a  part  of  blood.  By  absorp- 
tion is  meant  the  passage  of  the  digested  food  through  the  lining 
of  the  alimentary  canal,  and  through  the  thin  walls  of  the  count- 
less blood  vessels  and  lacteals  that  lie  close  at  hand.  To  under- 
stand this  process  we  must  first  consider  — 

The  Principles  of  Osmosis.1  —  An  apparatus  for  the  demon- 
stration of  osmosis  is  shown  in  Fig.  37.  Over  the  larger  end 
of  a  thistle  tube  is  tied  a  piece  of  the  intestine  of  a  sheep 
or  pig.  The  tube  is  half  filled  with  a  thick  solution  of  grape 
sugar  (honey  will  do  as  well),  and  is  inserted  in  a  bottle  filled 
with  water  to  the  level  of  the  grape  sugar.  The  height  of 
the  thistle  tube  is  increased  by  attaching  a  glass  tube.  At 
the  beginning  of  the  experiment  we  have  two  liquids  (water 

1  See  "Laboratory  Exercises,"  No.  23. 


idi 


STUDIES  IN  PHYSIOLOGY 


and  grape  sugar  solution)  of  different  density  (the  liquid 
within  the  thistle  tube  being  the  more  dense),  these  liquids 
separated  by  an  animal  membrane. 

On  examining  the  apparatus  after  several  hours,  we  find 
that  the  solution  within  the  thistle  tube  has  risen  several 
inches,  while  the  water  in  the  bottle  is  at  a  lower  level  than  it 
was  at  first.  It  is  evident  that  some  of  the  water  has  passed 
through  the  membrane  of  the  intestine,  and  has  mingled  with 

the  grape  sugar  solution. 
Another  fact  becomes  evi- 
dent when  we  boil  with 
Fehling's  solution  a  little 
liquid  in  the  bottle  outside 
the  thistle  tube.  The 
deep  red  color  of  the  mix- 
ture proves  the  presence 
of  grape  sugar.  Two  cur- 
rents, therefore,  have  been 
passing  through  the  ani- 
mal membrane,  but  from 
|P  the  level  of  the  two  liquids 
we  know  that  the  amount 

of  water  that  has  gone  into 
FIG.  37. — Apparatus    to    illustrate    the   .,       . ,  .    .,      .    , 

Principles  of  Osmosis.  the  thistle  tube  is  greater 

than  the  amount  of  grape 

sugar  solution  that  has  passed  out.  If  the  apparatus  is 
allowed  to  stand  for  several  days,  the  liquid  within  the  tube 
may  rise  to  a  height  of  several  feet.  From  the  preceding 
observations  we  derive  the  following  — 

Law  of  Osmosis.  —  When  two  liquids  of  different  density  are 
separated  by  an  animal  (or  plant}  membrane,  they  tend  to 
mingle,  and  the  greater  Jloiv  is  always  from  the  less  dense  to  the 
more  dense. 

Two  other  pieces  of  apparatus  similar  to  that  already 
described  should  be  prepared,  the  second  thistle  tube  being 
filled  with  a  rather  thin  starch  paste,  and  the  third  with 


THISTLE  TUBE       THISTLE  TUBE 

No.  1  No.  2 


THISTLE  TUBE 
NO.  3 


A   STUDY  OF   BLOOD   MANUFACTURE  103 

raw  white  of  egg  mixed  with  water.  At  the  end  of  several 
days  the  liquids  in  both  thistle  tubes  will  be  found  some- 
what higher  than  the  level  of  the  water  outside,  showing 
that  the  denser  starch  paste  and  proteid  mixtures  have 
absorbed  some  water.  But  when  we  test  the  water  outside 
the  starch  by  adding  iodine,  we  fail  to  find  a  trace  of  starch ; 
and  on  adding  nitric  acid  and  ammonia  to  the  water  in  the 
second  experiment,  we  demonstrate  that  little  or  none  of  the 
proteid  has  passed  through  the  intestine. 

We  have  found,  then,  that  some  substances  pass  readily 
through  an  animal  membrane  while  others  do  not.  To  the 
former  class  is  given  the  name  crys'tal-loids  because  many  of 
these  substances  have  a  crystalline  form.  As  examples  of 
crystalloids  we  may  mention  sugar,  salt,  water  (crystalline 
when  frozen),  and  peptones  (without  crystalline  form). 
Col'loids  (Greek  =  gluelike),  on  the  other  hand,  include 
proteids,  starch,  and  gum,  which  do  not  readily  soak  through 
an  inclosing  membrane. 

Application  of  the  Principles  of  Osmosis  to  Absorption.  —  We 
can  now  readily  see  the  necessity  for  the  change  of  starch 
into  sugar,  and  of  proteids  into  peptones,  and  for  the  emul- 
sion or  saponification  of  fats.  Unless  these  nutrients  are 
converted  from  colloids  into  crystalloids,  they  cannot  pass 
through  the  membranes  that  separate  them  from  the  blood. 
Although  absorption  cannot  be  wholly  explained  by  applying 
the  principles  of  osmosis,  yet  this  is  undoubtedly  one  of  the 
most  important  factors  in  the  process. 

The  most  favorable  conditions  for  rapid  absorption  are 
these :  (1)  a  considerable  extent  of  moist,  absorbing  mem- 
brane, (2)  a  rich  supply  of  blood  and  lymph  vessels  beneath 
this  membrane,  and  (3)  the  digested  food  must  remain  for 
some  time  in  close  contact  with  the  absorbing  surface. 
Keeping  in  mind  these  requirements,  let  us  consider  the 
opportunities  for  absorption  offered  in  each  region  of  the 
alimentary  canal. 

Absorption  in  the  Mouth,  Throat,  and  Gullet. — While  the 


104  STUDIES   IN  PHYSIOLOGY 

mouth,  throat,  and  gullet  all  have  a  moist  surface  generously 
supplied  with  blood  vessels,  the  food  does  not  lie  next  the 
mucous  membrane  for  any  considerable  time,  and  therefore 
the  amount  of  absorption  in  these  regions  is  not  great.  If 
one  eats  slowly,  some  of  the  dissolved  salts  and  sugars  and 
water  are  probably  absorbed  before  reaching  the  stomach. 

Absorption  in  the  Stomach.  —  In  the  stomach  the  food  usu- 
ally remains  for  several  hours,  and  one  would  therefore 
expect  that  a  good  deal  of  absorption  would  take  place  during 
this  time.  But  we  must  remember  that  the  contraction  of 
the  gastric  muscles  keeps  the  food  in  constant  motion.  This 
movement,  while  favorable  for  digestion,  diminishes  absorp- 
tion, because  the  liquefied  food  does  not  remain  long  enough 
in  one  place  to  soak  into  the  blood. 

Absorption  in  the  Small  Intestine.  —  We  therefore  find  that 
most  of  our  food  passes  out  of  the  stomach  before  it  is 
absorbed.  In  the  structure  of  the  small  intestine,  however, 
we  seem  to  find  every  possible  provision  for  gathering  up 
the  nutrients.  The  amount  of  surface  is  greatly  increased 
by  the  crescent-shaped  ridges,  and  still  more  by  the  villi, 
thousands  of  which  project  from  every  square  inch  of  the 
mucous  lining.  As  the  souplike  food  mass  is  pushed  slowly 
along  through  the  small  intestine,  it  becomes  less  and  less 
in  bulk,  and  more  and  more  solid,  owing  to  the  fact  that  the 
dissolved  salts,  sugars,  peptones,  and  fats  are  largely  taken 
up  by  the  blood  vessels  and  lacteals  within  the  villi. 

Absorption  in  the  Large  Intestine.  —  The  amount  of  absorp- 
tion in  the  large  intestine  is  considerably  less,  of  course,  for 
both  villi  and  crescentic  ridges  are  wanting.  Yet  even  here 
considerable  absorption  takes  place.  When  the  mass  in  the 
intestine  reaches  the  rectum,  it  consists  of  little  but  the 
indigestible  cellulose  of  vegetable  foods,  some  undigested 
connective  tissue,  waste  substances  from  the  bile,  the  solids 
in  the  mucous  secretion,  and  some  raw  starch  and  fats  if 
large  quantities  of  these  nutrients  have  been  eaten.  This 
refuse  of  the  food  is  thrown  off  from  the  body. 


A   STUDY  OF  BLOOD   MANUFACTURE 


105 


13.     SYNOPSIS  OF  DIGESTION 


EEGION  OF  ALI- 
MENTARY CANAL 

KIND  OF  SECRETION 

PRESENT 

PROCESSES  CARRIED  ON 

Mouth  cavity. 

Saliva  and  mucus. 

Mastication  of  food. 
Starch  changed  to  sugar. 
Sugar  and  salt  dissolved. 
Tasting  of  food  substances. 
Small  amount  of  absorption  of 
water,  salt,  sugar. 

Throat  cavity. 

Mucus. 

Passage  of  food  and  air. 

Esophagus. 

Mucus. 

Passage  of  food  to  the  stomach. 

Stomach. 

Gastric  juice,  con- 
sisting of  water, 
pepsin,  and  hy- 
drochloric acid, 
and  mucus. 

Churning  of  food  by  the  muscles. 
Proteids  changed  to  peptones. 
Insoluble  salts  changed  to  soluble. 
Small  amount  of  absorption  of 
water,  salts,  sugars,  peptones. 

Small  intes- 
tine. 

Pancreatic  juice, 
bile,  intestinal 
juices,  and 
mucus. 

Fats  changed  to  emulsion  and  to 
soap  and  glycerin. 
Starch  changed  to  sugar. 
Proteids  changed  to  peptones. 
Large  amount  of  absorption  of 
fats  by  lacteals  of  villi. 
Large  amount  of  absorption  of 
water,   salt,  sugar,    peptones, 
by  blood  vessels  of  villi. 

Large  intes- 
tine. 

Mucus,  and  in- 
testinal juices. 

Small  amount  of  absorption  of 
nutrients. 
Removal  of  refuse  of  food  from 
the  body. 

106  STUDIES  IN  PHYSIOLOGY 

14.   THE  HYGIENE  OF  DIGESTION 

Importance  of  Subject.  —  "I  have  come  to  the  conclusion/' 
says  Sir  Henry  Thompson,  a  noted  English  physician,  "  that 
more  than  half  the  disease  which  embitters  the  middle  and 
latter  part  of  life  is  due  to  avoidable  errors  in  diet,  .  .  .  and 
that  more  mischief  in  the  form  of  actual  disease,  of  impaired 
vigor,  and  of  shortened  life  accrues  to  civilized  man  ...  in 
England  and  throughout  central  Europe  from  erroneous  habits 
of  eating  than  from  the  habitual  use  of  alcoholic  drink,  con- 
siderable as  I  know  that  evil  to  be."  This  statement  may 
not  be  literally  true  of  conditions  here  in  America,  but  it 
should  at  least  call  our  attention  to  the  great  importance 
of  the  hygiene  of  digestion.  Dyspepsia  in  its  many  differ- 
ent forms,  typhoid  fever,  jaundice,  gout,  not  to  mention  the 
more  common  disorders  of  colic,  cholera  morbus,  and  con- 
stipation, are  but  a  few  of  the  ills  afflicting  mankind,  all  of 
which  might  be  avoided  by  eating  proper  food  in  a  proper 
manner. 

Hygienic  Habits  of  Eating.  —  One  should  form  the  habit,  in 
the  first  place,  of  eating  slowly  and  of  thoroughly  masticat- 
ing each  mouthful  of  food.  The  great  English  statesman 
Gladstone,  who  retained  his  vigor  in  old  age  to  a  remark- 
able degree,  is  said  to  have  had  the  habit  of  biting  each 
mouthful  of  food  thirty-two  times ;  for  in  this  way,  he  said, 
he  gave  each  tooth  a  chance  to  work  upon  it.  If  one  fol- 
lowed such  a  rule,  the  stomach  and  other  organs  of  diges- 
tion would  be  relieved  of  work  which  they  are  not  fitted 
to  perform,  and  thus  one  would  doubtless  escape  many  an 
attack  of  indigestion. 

The  process  of  chewing  likewise  stimulates  the  flow  of 
saliva.  Saliva  not  only  helps  digest  food  in  the  mouth, 
but  this  juice  also,  when  swallowed  with  the  food,  incites 
the  gastric  glands  to  greater  activity.  At  least  a  half  hour 
should  be  devoted  to  the  eating  of  dinner  and  fifteen  to 
twenty  minutes  to  breakfast  and  lunch  or  supper.  The 


A  STUDY   OF  BLOOD   MANUFACTURE  107 

proper  digestion  of  food  depends  in  no  small  degree  upon 
one's  mental  state ;  worry  and  disagreeable  topics  should, 
therefore,  be  forgotten  so  far  as  possible  while  one  is  eating, 
and  the  mealtime  should  be  made  a  season  of  enjoyment. 

Regular  hours  of  eating  are  of  great  importance,  for  noth- 
ing more  commonly  deranges  the  digestive  system  than  the 
continual  nibbling  of  food  or  sweetmeats  between  meals. 
One  should  refrain  from  vigorous  exercise  or  mental  exertion 
for  a  half  hour  or  more  after  eating ;  the  reason  for  this  will 
be  clear  after  a  study  of  the  blood  system. 

Care  of  the  Teeth.  —  Too  mugh  stress  cannot  be  laid  on 
the  importance  of  caring  for  the  teeth,  since  decaying 
teeth  are  frequently  painful,  they  are  always  unsightly  and 
are  usually  the  cause  of  an  ill-smelling  breath,  and  they 
often  lead  to  other  derangements  of  the  alimentary  canal. 
Immediately  after  eating  one  should  brush  the  teeth  thor- 
oughly on  all  sides,  using  warm  water  and  a  little  castile 
soap  or  an  alkaline  tooth  powder,  and  should  make  sure 
that  bits  of  food  are  not  left  to  decay  between  the  teeth. 
The  frequent  use  of  dental  floss  or  silk  to  clean  the  spaces 
between  the  teeth  is  essential.  Pins,  knifeblades,  or  other 
metallic  implements,  however,  should  never  be  used  for  this 
purpose.  In  the  process  of  decomposition  to  which  we  have 
referred,  acids  are  formed  that  eat  away  enamel  and  den- 
tine, and  a  cavity  when  once  begun  grows  rapidly  unless  the 
decay  is  stopped.  For  this  reason  alkaline  tooth  powders 
are  recommended  to  counteract  the  possible  effects  of  acids. 
A  dentist  should  be  consulted  at  least  once  a  year,  in  order 
that  the  "  tartar  "  may  be  removed  and  the  cavities  filled  while 
they  are  small.  The  teeth  ought  never  to  be  used  to  crack 
nuts  or  to  pull  out  nails,  for  while  the  enamel  is  a  very  hard 
substance,  it  is  also  brittle  and  can  be  cracked  or  broken  off 
by  such  treatment ;  if  once  lost  it  will  not  grow  again. 

Adaptation  of  Foods  to  Individual  Needs.  —  The  growing  child 
should  be  supplied  with  a  simple  diet  composed  of  milk, 
cereals,  eggs,  bread,  and  fruits,  and  parents  should  exercise 


108  STUDIES  IN  PHYSIOLOGY 

great  care  to  prevent  boys  and  girls  from  eating  indiges- 
tible compounds.  It  is  of  course  impossible  in  a  few 
words  to  give  anything  like  a  complete  account  of  the  rela- 
tion of  food  to  the  needs  of  various  individuals.  One  person 
finds,  for  instance,  that  for  some  reason  he  cannot  eat  straw- 
berries or  cucumbers.  Since  these  foods  act  like  a  poison 
in  his  system,  they  must  of  course  be  avoided.  The  regula- 
tion of  diet  in  time  of  sickness  is  a  most  important  aid 
to  recovery.  In  certain  diseases  it  is  necessary  that  some 
kinds  of  food  should  be  forbidden,  Whenever  the  functions 
of  the  body  are  not  carried  pn  with  their  accustomed  vigor, 
the  physician  prescribes  foods  that  are  easily  digested,  —  for 
example,  milk,  raw  oysters,  toasted  bread,  and  soft-boiled 
eggs. 

Prevention  of  Constipation.  —  Constipation,  or  the  stoppage 
of  the  refuse  of  the  food  in  the  intestine,  is  one  of  the  most 
frequent  causes  of  discomfort,  and  to  insure  a  state  of  health 
the  useless  residue  should  be  expelled  from  the  large  in- 
testine regularly  each  day.  Constipation  may  usually  be 
counteracted  by  liberal  drinking  of  water,  especially  a  half 
hour  before  breakfast,  and  by  eating  foods  with  laxative 
effect,  —  for  example,  ripe  fruits  (especially  figs),  green 
vegetables,  and  breads  made  of  the  coarser  graham  and 
rye  flours. 

The  Use  of  Patent  Medicines.  —  The  enormous  sale  of  patent 
medicines,  soothing  sirups,  and  "  pain  killers  "  in  our  country 
is  a  source  of  incalculable  harm.  It  is  easy  enough  for  the 
makers  of  these  nostrums  to  describe  the  symptoms  of  the 
disease  which  the  medicine  is  warranted  to  cure,  and  so 
create  a  greater  demand  for  it.  Too  often,  as  we  have  seen 
(p.  39),  these  compounds  contain  alcohol,  morphine,  or 
other  dangerous  ingredients.  They  should  never  be  given, 
however  highly  recommended,  without  the  advice  of  a  com- 
petent physician.  When  an  attack  of  sickness  does  not 
readily  yield  to  a  treatment  of  diet  and  rest,  it  is  always 
safer  and  more  economical  in  the  end  to  consult  the  family 


A   STUDY   OF   BLOOD    MANUFACTURE  109 

physician  and,  what  is  of  equal  importance,  to  follow  his 
directions  implicitly. 

Effects  of  Alcoholic  Drinks  on  the  Organs  of  Digestion. — Alco- 
hol, unlike  most  of  the  substances  taken  into  the  alimentary 
canal,  requires  no  digestion.  It  can,  therefore,  be  absorbed 
very  rapidly  by  the  blood,  and  hence  alcohol  is  probably 
sometimes  of  great  value  when  administered  by  physicians, 
in  cases  when  ordinary  food  cannot  be  digested.  In  health, 
however,  alcoholic  drinks  must  be  regarded  as  an  expensive 
and  extremely  dangerous  source  of  energy. 

According  to  the  best  authorities,  small  quantities  of 
alcohol  (when  sufficiently  diluted)  seem  for  an  adult  to 
stimulate  an  increased  flow  of  saliva  and  gastric  juice. 
The  time  required  for  the  digestion  of  food,  when  alcohol 
is  present,  in  these  small  quantities,  does  not  seem  to  be 
increased.  Entirely  different  effects  follow,  however,  when 
strong  distilled  liquors  are  taken,  and  alcohol  in  any  large 
quantity  often  produces  serious  disturbances  of  the  organs 
of  digestion.  This  is  especially  true  when  liquors  are  taken 
without  food,  that  is,  between  meals.  The  constant  danger 
that  the  moderate  use  of  beer  and  the  light  wines  will  lead  to 
an  uncontrollable  thirst  for  alcohol  cannot  be  emphasized  too 
strongly.  All  authorities  agree,  too,  that  the  growing  youth 
should  let  alcohol  entirely  alone. 

15.    A  COMPARATIVE  STUDY  OF  DIGESTION 

A  Study  of  Teeth.  — Among  the  various  groups  of  inverte- 
brates, one  finds  structures  that  have  a  function  more  or 
less  like  that  of  teeth.  Beetles  and  grasshoppers,  for  ex- 
ample, have  two  horny  jaws  that  move  from  side  to  side, 
which  they  use  to  bite  their  food.  In  the  mouth  of  the 
lobster  and  crayfish  similar  structures  are  found,  and  in 
addition  these  animals  have  strong  teeth  in  the  stomach 
that  grind  against  one  another.  This  arrangement  is  called 
a,  "gastric  mill."  Many  snails  have  a  great  number  of  mi- 


110  STUDIES  IN  PHYSIOLOGY 

nute  teeth  upon  the  tongue.  In  obtaining  their  food  the;y 
use  this  rough  movable  tongue  like  a  file. 

Among  the  vertebrates  teeth  are  wanting  in  all  birds,  in 
toads,  turtles,  and  tortoises.  Most  of  these  animals,  how- 
ever, have  horny  beaks  that  aid  them  in  crushing  their 
food.  Frogs  have  teeth  along  the  upper  jaw  and  on  the 
roof  of  the  mouth  (see  Fig.  83)  ;  these  teeth  are  used  prin- 
cipally to  prevent  their  prey  from  escaping  and  to  aid  in 
swallowing.  In  rattlesnakes  and  other  venomous  reptiles 
two  or  more  long,  sharp  fangs  project  from  the  upper  jaw. 
These  contain  a  tube  through  which  is  forced  the  poison 
secreted  in  the  poison  glands  near  the  root  of  the  tooth. 
When  the  snake  strikes  at  its  victim,  the  sharp  ends  of 
the  fangs  are  buried  in  the  flesh,  and  the  poison  is  left  in 
the  wound. 

In  some  of  the  groups  of  mammals  (that  is,  animals  which 
are  covered  with  hair)  certain  types  of  teeth  are  developed 
to  an  extraordinary  degree,  and  by  these  teeth  the  animal 
is  especially  adapted  for  securing  and  masticating  its  par- 
ticular kind  of  food.  Eabbits,  squirrels,  rats,  and  beavers 
have  long  chisel-shaped  incisors  which  enable  them  to  obtain 
their  food  by  gnawing.  These  incisors  grow  throughout 
the  life  of  the  animal  and  are  kept  sharp  by  a  constant  grind- 
ing upon  each  other  of  the  cutting  edges.  Canine  teeth  are 
altogether  wanting  in  these  rodents  (Latin  rodere  =  to  gnaw). 
Following  is  the  dental  formula  of  the  rabbit  :  — 


Canine  teeth  are  specially  fitted  to  tear  in  pieces  fleshy 
tissue,  and  they  reach  their  greatest  development  in  the 
group  of  car-niv'o-ra  or  flesh-eaters.  The  long,  conical  teeth 
in  the  jaws  of  the  dog,  cat,  lion,  and  tiger  are  canines. 
All  the  teeth  of  the  carnivora  have  pointed  crowns  adapted 
for  tearing  and  cutting,  rather  than  for  grinding.  A  most 
striking  example  of  canine  teeth  is  furnished  by  the  huge 


A   STUDY   OF  BLOOD   MANUFACTURE  111 

tusks  of  the  walrus.     The  arrangement  of  teeth  in  the  mouth 
of  a  dog  is  represented  in  the  dental  formula, 

.3  +  3      1+1-4+4  TO2+2_42 
'  ~ 


Iii  the  group  of  the  her-biv'o-ra}  which  includes  the  animals 
that  feed  wholly  upon  vegetation,  the  huge  premolars  and 
molars  are  of  special  use  ;  they  grind  up  the  grass  and  grain 
like  millstones.  A  horse's  dentition  is  represented  by  the 
formula, 

3+3      1+1       4+4        3+3  _dl 
3+3'     T+i'  P  4+4:'      S+S~ 

The  incisors  of  a  horse  are  well  developed,  but  the  canines 
seldom  push  through  the  gums.  In  the  space  between  the 
incisors  and  premolars,  man  puts  the  horse's  bits.  A  cow 
has  no  incisors  in  the  upper  jaw,  and  the  canines  are  also 
wanting. 

Since  man  has  all  of  the  four  kinds  of  teeth  developed  in 
about  equal  proportions,  he  is  evidently  well  fitted  to  eat 
both  animal  and  vegetable  tissues,  and  a  well-rounded  diet 
should  include  a  great  variety  of  food  materials. 

The  Tongue  in  Other  Animals.  —  The  tongue  of  frogs  and 
toads  is  attached  just  inside  the  mouth  opening,  and  its  free 
end,  when  the  mouth  is  closed,  extends  backward  toward 
the  gullet.  In  securing  the  insects  upon  which  it  largely 
feeds,  the  animal  opens  its  mouth  and  thrusts  forward  the 
sticky  end  of  the  tongue,  which  captures  the  fly  or  bee.  The 
end  of  the  tongue  is  then  quickly  withdrawn  into  the 
mouth,  and  the  food  is  swallowed  at  once.  The  snake  uses 
its  forked  tongue  principally  as  an  organ  of  feeling,  darting 
it  from  its  mouth  with  great  rapidity.  This  tongue  is  per- 
fectly harmless.  Among  the  carnivora  the  upper  surface 
of  the  tongue  is  covered  with  strong  papillae.  This  enables 
the  dog,  cat,  lion,  or  tiger  to  scrape  the  meat  from  bones 
and  to  extract  the  marrow  after  the  bones  are  broken  open. 


112 


STUDIES   IN  PHYSIOLOGY 


---Mouffr 


fftffry/?* 


ope/7//fgs 
Ganglia  co/ist/tt/t/ng-  ~  ~ . 


dosser?  surface.  x 


FIG.  38.  —  The  Earthworm. 

A  =  side  view  of  an  earthworm. 

B  =  dorsal  view  of  a  dissected  earthworm. 

(7  =  longitudinal  section  of  an  earthworm. 

The  Alimentary  Canal  of  the  Earthworm.  —  At  the  anterior 
end  of  the  worm  is  a  small  slitlike  mouth  opening,  which 
communicates  with  the  pharynx.  By  means  of  this  more  or 
less  barrel-shaped  organ  the  animal  sucks  in  its  food.  Pos- 


A   STUDY  OF  BLOOD   MANUFACTURE 


113 


terior  to  the  pharynx  is  the  gullet ;  it  extends  from  about 
the  sixth  to  the  fifteenth  joint  of  the  body,  and  there  opens 
into  a  thin-walled  enlargement  of  the  alimentary  canal 
called  the  crop.  From  this  storage  sac  the  food  mass  is 
passed  on  into  a  muscular  gizzard,  where  it  is  rolled  about 
and  ground  to  prepare  it  for  digestion.  The  remainder  of 
the  food  canal, 
the  stomach  intes- 
tine) extends  from 
the  nineteenth 
joint  to  the  end 
of  the  body.  Here 
the  food  is  di- 
gested and  ab- 
sorbed, 

The  Alimentary 

Canal  Of  the  Frog.  FIG.  39.  —  Internal  Organs  of  the  Frog. 

—  In  the  frog  we 
fin  d  a  more  highly 
developed  alimen- 
tary canal  than 
that  just  de- 
scribed. Seven 
openings  com- 
municate with  the 
mouth  cavity,  cor- 
responding  in 

function  to  the  seven  in  the  throat  of  man.  These  open 
ings  are  as  follows:  two  from  the  nostrils,  the  mouth 
opening,  two  communicating  with  the  ear  cavities  through 
the  Eustachian  tubes,  the  opening  into  the  gullet,  and 
the  glottis  (opening  into  the  larynx).  The  frog,  there- 
fore, has  no  distinct  throat  cavity.  A  short  gullet  conducts 
the  food  into  the  cylindrical  stomach,  and  a  somewhat 
coiled  intestine  communicates  with  the  exterior  of  the  body 
through  the  rectum.  The  frog  has  a  well-developed  liver, 


a  =  stomach. 
6  =  urinary  bladder. 
c  =  small  intestine. 
d  =  large  intestine. 
e  —  liver. 
/=bile  duct. 
g  =  gall  bladder. 
h  =  spleen. 
i  =  lung. 
k  =  larynx. 
I  =  fat  body. 
m  =  spermary. 
n  =  ureter. 


o  =  kidney. 
p  =  pancreas. 
r  =  pelvic  girdle.  * 
s  =  cerebral 

hemisphere. 
sp  =  spinal  cord. 
t  =  tongue. 
u  —  auricle. 
v  =  ventricle. 
w  =  optic  lobe. 
x  =  cerebellum. 
y  =  Eustachian  recess. 
z  =  nasal  sacs. 


114 


STUDIES  IN  PHYSIOLOGY 


beneath  which  is  a  green  gall  bladder.  A  pancreas  is  like- 
wise present,  which,  as  in  man,  pours  its  secretions  through 
the  common  bile  duct  into  the  small  intestine.  The  alimen- 
tary canal  of  the  frog  is  several  times  the  length  of  the 
body,  and  hence  it  is  more  or  less  coiled.  This  increased 
length  provides  a  greater  surface  for  digestion  and  ab- 
sorption. 

The  Alimentary  Canal  of  the  Pigeon.  —  Striking   modifica- 


Cer*6ra/ 
'  fiem/spfteres 


---Gutter 
---Crop 
" "-  <5yr/'nx 
"-/tight avr/'c/e 


FIG.  40.  —  Longitudinal  Section  of  a  Bird. 

tions,  due  to  the  absence  of  teeth  in  the  mouth,  are  seen  in  the 
digestive  apparatus  of  birds.  In  the  first  place,  the  gullet 
is  relatively  large  to  allow  the  passage  of  the  more  or  less 
solid  food.  Two  thirds  of  the  way  down  the  gullet  on  its 
ventral  surface  is  a  saclike  enlargement  of  considerable  size 


A   STUDY   OF  BLOOD   MANUFACTURE  115 

called  the  crop.  Here  the  food  is  softened  somewhat,  and  then 
it  is  passed  on  into  the  stomach.  This  organ  consists  of  &  pro- 
ven-trie'u-lus  (Latin  pro  =  before  +  ventriculus  =  little  stom- 
ach), the  walls  of  which  contain  a  large  number  of  gastric 
glands,  and  a  thick-walled,  muscular  gizzard,  which  has  a  horny 
lining.  In  the  gizzard  the  food  is  ground,  and  this  process 
is  assisted  by  the  small  stones  that  the  bird  swallows.  The 
intestine  leaves  the  gizzard  close  to  the  opening  from  the 
pro  ventriculus,  and  forms  a  loop  inclosing  the  pancreas. 
The  rest  of  the  intestine  is  coiled  in  a  more  or  less  spiral 
fashion.  A  gall  bladder  is  absent;  the  bile  ducts  for  this 
reason  pass  directly  from  the  right  and  left  lobes  of  the 
liver  into  the  intestine. 

The  Alimentary  Canal  of  the  Sheep.  —  The  majority  of  mam- 
mals have  as  a  „. 
stomach  a  simple 
sac.  But  in  some 
of  the  hoofed 
animals  (cattle, 
sheep,  goats,  deer), 
this  organ  reaches 
a  high  degree  of 
complexity.  The  FIG.  41.  — Stomach  of  an  Ox  (opened  to  show 
grass  eaten  by  Chambers). 

these    animals    is          a  =  esophagus,  d  =  psalterium. 

i       .,T         -,.  6  =  rumen.  e  =  abomasum. 

mixed  with  saliva         c  =  reticulum.  /=  small  intestine. 

and    swallowed 

without  mastication  into  a  large  sac  called  the  ru'men.  It  is 
either  stored  here  or  is  passed  on  to  a  second  sac,  called  from 
its  honeycombed  wall  the  re-tic'u-lum.  When  the  sheep  or 
cow  has  finished  eating,  the  food  in  rounded  masses  is 
forced  back  in  lumps  through  the  esophagus  into  the  mouth 
cavity,  and  is  then  thoroughly  masticated.  To  this  process 
is  given  the  name  cud-chewing  or  ruminating.  The  pasty 
mass  is  now  swallowed  a  second  time,  passing  almost  imme- 
diately into  a  third  compartment  of  the  stomach,  the  psal- 


116  STUDIES  IN  PHYSIOLOGY 

terri-um.  After  being  strained  between  the  leaflike  plates 
of  mucous  membrane  in  this  sac,  it  enters  the  fourth  and 
last  chamber,  called  the  ab-o-ma'sum.  This  is  the  real  diges- 
tive portion  of  the  stomach.  The  other  sacs  should  be 
regarded,  like  the  crops  of  birds,  as  enlargements  of  the 
esophagus  that  serve  as  storage  reservoirs.  The  rennet 
used  in  making  cheese  is  prepared  from  the  lining  of  the 
abomasum  of  a  calf.  The  wall  of  the  rumen  and  reticulum 
of  cud-chewing  animals  is  eaten  in  the  form  of  tripe.  The 
intestines  of  the  ox  have  the  astonishing  length  of  one  hun- 
dred and  fifty  feet.  Since  the  food  of  the  animal  is  wholly 
vegetable,  a  much  longer  time  is  required  for  its  digestion, 
and  hence  the  great  extent  of  the  intestines.  Carnivorous 
animals,  on  the  other  hand,  have  a  relatively  short  alimen- 
tary canal. 

Comparison  of  the  Digestive  Organs  Studied.  —  The  striking 
characteristic  of  the  digestive  apparatus  of  the  earthworm 
is  its  simplicity.  A  straight  tube  extends  from  one  end  of 
the  body  to  the  other,  with  several  enlargements  in  which 
certain  processes  are  carried  on.  Digestive  glands  corre- 
sponding to  the  liver  and  pancreas  of  man  are  altogether 
wanting.  In  the  other  animals  that  we  have  considered  an 
increasing  complexity  of  structure  is  seen  until  we  come  to 
the  highly  specialized  alimentary  canal  of  the  ruminants. 
In  every  example  studied  the  digestive  organs  have  become 
specially  fitted  to  digest  the  kind  of  food  the  animal  eats. 


CHAPTER   VII 
A  STUDY  OF  THE  BLOOD 

1.  USES  OF  THE  BLOOD 

Nutrition  in  the  Amoeba.  —  The  process  of  nutrition  in  the 
amoeba  is  relatively  simple.  When  the  single  cell,  by  push- 
ing out  its  false  feet,  comes  in  contact  with  a  bit  of  food, 
the  protoplasm  of  the  animal  slowly  flows  about  the  food 


FIG.  42. —  An  Amoeba  taking  in  a  Particle  of  Food. 

particle  until  the  latter  is  surrounded.  Once  within  the 
cell,  the  food  is  digested  by  the  living  substance,  and,  as 
the  animal  is  continually  altering  its  shape,  this  digested 
food  is  easily  moved  from  one  part  of  the  cell  to  another. 
The  animal  is  so  small  it  has  no  need  of  a  specially  devel- 
oped alimentary  canal  or  blood  system.  Oxygen  is  absorbed 
by  the  protoplasm  as  fast  as  it  is  needed,  and  the  waste 
matters  (carbon  dioxid,  water,  and  urea),  that  are  always 
formed  in  living  substance,  are  given  off  by  the  amoeba  as 
fast  as  they  are  produced.  Every  part  of  the  cell  may  be 
said  to  perform  the  functions  of  mouth,  stomach,  and  intes- 
tine, of  blood,  respiratory,  and  excretory  systems. 

Nutrition   in   Man.  —  In  the  human  body,  on  the  other 
hand,  we  find  special  organs,  each  devoted  to  but  one  of  the 

117 


118  STUDIES  IN  PHYSIOLOGY 

functions  we  have  just  enumerated.  The  alimentary  canal 
prepares  the  digested  food,  the  lungs  supply  us  with  oxygen, 
while  the  waste  matters  are  excreted  by  the  kidneys,  lungs, 
and  skin.  But  every  cell  of  the  body,  as  was  the  case  in 
the  amoeba,  requires  a  supply  of  nutrients  and  oxygen,  and 
in  every  bit  of  living  substance  waste  materials  are  being 
constantly  formed  by  metabolism.  Since  many  tissues  of  the 
body  are  at  a  considerable  distance  from  the  organs  of  diges- 
tion, respiration,  and  excretion,  we  can  see  that  some  means 
must  be  provided  for  bringing  all  these  organs  into  commu- 
nication with  each  other.  This  is  effected  by  the  blood, 
which  is  pumped  through  blood  vessels  by  the  heart.  In 
this  way  blood  is  able  to  serve  the  needs  of  every  tissue  of 
the  body. 

Uses  of  the  Blood.  —  Blood,  therefore,  has  four  important 
functions:  (1)  it  carries  the  digested  food  from  the  alimen- 
tary canal  to  the  various  tissues  that  need  it;  (2)  it  absorbs 
oxygen  in  the  lungs  and  distributes  this  gas  to  the  working 
tissues  ;•  (3)  it  receives  from  the  cells  of  the  body  the  carbon 
dioxid,  water,  and  urea  that  are  produced  by  oxidation,  and 
carries  these  wastes  to  the  excretory  organs,  by  which  they 
are  thrown  out  of  the  body ;  (4)  it  helps  also  to  equalize  the 
temperature  of  the  different  parts  of  the  body. 

2.  A  STUDY  OF  BEEF-BLOOD  l 

Preparation.  —  Blood  is  much  the  same  in  all  mammals, 
and  so  we  can  learn  a  great  deal  in  regard  to  this  important 
tissue  in  our  own  body  by  studying  the  blood  of  a  cow.  One 
can  secure  at  any  slaughterhouse  beef-blood,  which  should 
be  allowed  to  flow  from  the  animal  into  a  bottle,  and  to  stand 
in  a  cold  place  undisturbed  for  several  days.  When  first 
drawn  from  the  animal,  it  is  a  liquid  of  bright  red  color,  but 
it  soon  changes  to  a  dark  maroon. 

Blood  Clot.  —  Other  changes  are  likewise  noticeable.     At 

1  See  "Laboratory  Exercises,"  No.  25. 


A   STUDY   OF  THE   BLOOD  119 

the  end  of  a  few  moments  the  blood  becomes  viscid ;  it  soon 
thickens  to  the  consistency  of  jelly,  and  if  the  bottle  be 
now  inverted,  none  of  the  blood  will  escape.  An  examina- 
tion made  at  the  end  of  several  hours  shows  that  the  jelly- 
like  mass  is  gradually  shrinking  in  size  iintil  finally  it  comes 
to  occupy  about  half  the  capacity  of  the  bottle.  This  dark 
red  mass  is  called  the  blood  clot,  which  retains  the  shape  of 
the  bottle,  and  by  its  form  and  color  reminds  one  of  a  jar 
of  currant  jelly. 

Blood  Serum.  —  If  the  blood  is  not  disturbed  for  several 
days,  a  transparent,  straw-colored  liquid  will  be  seen  sur- 
rounding the  clot  and  filling  the  other  part  of  the  space  in 
the  bottle.  To  this  liquid  is  given  the  name  blood  serum. 
Blood,  then,  when  taken  from  the  body  becomes  separated  into 
two  nearly  equal  portions,  the  jellylike  clot  and  the  liquid  serum, 
and  to  this  process  of  separation  is  given  the  name  co-ag-u-la'tion 
or  blood  clotting. 

Cause  of  Coagulation. — When-  one  examines  with  a  com- 
pound microscope  a  drop  of  fresh  beef -blood,  red  and  white 
corpuscles  similar  to  those  described  in  human  blood  (see 
p.  25),  are  seen  floating  in  the  liquid  plasma.  In  a  short 
time,  however,  little  threadlike  fibers  make  their  appearance 
in  the  serum,  and  extend  in  all  directions  across  the  drop. 
These  soon  shorten.  In  this  process  the  red  and  white  cor- 
puscles are  gathered  together  as  though  caught  in  the  threads 
of  a  net.  The  liquid  serum,  meanwhile,  is  squeezed  out  of 
the  mass.  This  same  process  takes  place  in  the  bottle  of 
beef-blood.  The  fibers  at  first  extend  from  one  side  of  the 
glass  to  the  other,  thus  forming  a  more  or  less  solid  mass, 
which  holds  the  blood  in  the  bottle,  even  when  it  is  inverted. 
The  fibers  soon  shorten  and  lose  their  hold  upon  the  glass, 
and  by  their  shrinkage  the  cylindrical  clot  is  formed. 
.  Blood  Fibrin.  —  We  have  seen  that  coagulation  is  caused 
by  the  fine  threads  that  appear  spontaneously  as  soon  as 
blood  is  shed.  Still  clearer  proof  that  this  is  the  fact  is 
furnished  by  the  following  experiment.  Get  the  butcher  at 


120  STUDIES  IN  PHYSIOLOGY 

the  slaughterhouse  to  catch  a  quart  of  freshly  drawn  blood, 
and  to  stir  it  vigorously  for  several  minutes  with  a  bunch  of 
twigs  or  a  broom.  On  examining  the  twigs  one  sees  that 
they  are  covered  with  a  stringy  mass.  When  this  is  washed, 
it  is  found  to  be  composed  of  white  elastic  fibers,  like  those 
we  saw  forming  in  the  drop  of  blood  under  the  compound 
microscope.  By  testing  this  so-called  blood  fibrin  with  nitric 
acid  and  ammonia,  we  demonstrate  it  to  be  a  kind  of  proteid. 

Defibrinated  Blood.  —  After  the  fibrin  has  been  removed,  a 
red  liquid  remains  that  looks  like  the  normal  blood.  But 
however  long  it  is  allowed  to  stand,  it  will  never  clot.  The 
name  de-fi'bri-na-ted  blood  (Latin  de  =  without  +fibriri)  is 
given  to  this  liquid.  So  then  we  have  proved  in  two  differ- 
ent ways  that  the  clotting  of  blood  is  due  to  blood  fibrin. 

Difference  between  Blood  Plasma  and  Blood  Serum.  — We 
have  called  the  freshly  drawn  liquid  in  which  the  blood  cor- 
puscles float,  the  blood  plasma,  and  the  straw-colored  liquid 
surrounding  the  clot,  blood  serum.  While  the  appearance 
of  both  liquids  under  the  compound  microscope  is  much  the 
same,  they  differ  in  one  particular :  blood  plasma  clots,  blood 
serum  does  not.  Or  to  describe  their  difference  in  composi- 
tion, we  may  say  that  blood  serum  is  blood  plasma  minus 
fibrin. 

The  question  naturally  presents  itself,  Why  does  not 
blood  plasma  clot  when  it  is  in  the  body?  Physiologists 
have  demonstrated  that  coagulation  is  not  due  to  the  fact 
that  the  blood  has  ceased  to  be  in  motion,  nor  is  it  caused  by 
exposure  to  the  air.  It  is  known  that  a  liquid  proteid  called 
fi-brin'o-gen  (Latin  fibrin-}- gen = maker)  is  found  in  blood 
plasma,  and  that  this  is  changed  into  solid  fibrin  when  a 
clot  is  formed.  But  why  this  change  does  not  take  place  as 
long  as  the  blood  is  within  a  healthy  blood  vessel,  has  not 
been  satisfactorily  explained. 

Composition  of  Blood  Serum. — Blood  serum  contains  over 
90  %  of  water,  in  which  are  dissolved  the  various  nutrients 
obtained  by  absorption  from  the  alimentary  canal.  The 


A  STUDY   OF  THE  BLOOD  121 

presence  of  each  of  these  nutrients  in  the  beef  serum  may 
be  demonstrated  by  applying  the  various  tests  given  on 
pp.  44_46.  Thus,  if  a  small  portion  of  the  serum  be  put 
into  a  test  tube  and  heated,  it  coagulates,  showing  that  pro- 
teids  are  present.  The  occurrence  of  mineral  matters  is 
proven  by  the  ash  that  is  left  after  blood  is  burned.  Grape 
sugar  and  fats  are  likewise  present,  though  in  smaller 
quantities  than  one  would  expect.  Starch  is,  of  course, 
absent. 

Change  in  Blood  on  mixing  with  Oxygen.  —  When  the  blood 
passes  through  the  lungs,  as  already  stated,  it  absorbs  oxy- 
gen. The  resulting  change  in  color  can  be  seen  from  the 
following  experiment.  Pour  a  small  amount  of  defibrinated 
blood  into  a  glass  bottle  and  stopper  tightly.  When  the 
bottle  is  shaken  vigorously,  the  blood  is  mixed  with  the  oxy- 
gen in  the  bottle,  and  the  dark  maroon  color  changes  almost 
instantly  to  a  bright  scarlet.  The  same  change  in  color 
takes  place  when  the  serum  is  poured  off  and  the  blood  clot 
is  exposed  to  the  air. 

3.   HUMAN  BLOOD 

Application  of  the  Study  of  Beef -blood.  —  All  of  the  facts 
learned  from  the  preceding  study  of  beef-blood  are  equally 
true  of  human  blood.  As  soon  as  it  flows  from  the  body, 
the  fibrinogen  changes  to  fibrin,  and  thus  a  clot  is  formed. 
Coagulation  is  of  great  practical  importance,  since  it  provides 
a  natural  means  of  closing  up  injured  blood  vessels,  and  of 
preventing  loss  of  blood. 

Red  Blood  Corpuscles.  —  The  form  and  size  of  red  blood 
corpuscles  have  been  already  discussed  in  connection  with 
the  study  of  the  cellular  structure  of  the  body  (see  p.  26). 
When  highly  magnified  they  appear  as  circular  disks,  the 
color  of  which  is  not  red,  as  one  would  expect,  but  yellowish. 
The  deep  red  color  of  the  blood  is  due  to  the  fact  that  every 
drop  contains  such  a  countless  number. 

Like  other  cells  they  are  composed  of  protoplasm.    Chemt 


122 


STUDIES  IN  PHYSIOLOGY 


^8,%°C»^o 


cal  analysis  shows  the  presence  of  50  %  of  water  and  a 
small  amount  of  mineral  matter.  But  the  most  important 
ingredient  is  a  proteid  substance  called  hem-o-glo'bin  (see 
p.  18).  This  compound  contains  iron,  and  constitutes  over 
35  °/o  of  red  corpuscles.  Hemoglobin  gives  the  red  color 
to  the  blood  and  has  the  remarkable  power  of  combining 
with  oxygen  when  that  element  is  abundant,  and  of  giving 
it  up  wherever  it  is  needed  in  the  various  parts  of  the 
body.  We  may,  therefore,  compare  the  blood  corpuscles  to 

countless  little  boats, 
floating  in  a  stream  of 
plasma ;  they  take  on 
their  cargo  of  oxygen 
from  the  air  in  the 
lungs  and  discharge 
it  to  the  cells  of  the 
tissues.  Wrorn-out  cor- 
puscles are  destroyed 
in  the  liver  and  spleen, 

\u    yjy  an(j    their    place     is 

P/  taken    by   new    ones, 

which  are  produced, 
as  we  shall  learn,  by 
cells  in  the  red  mar- 
row of  bones. 

White  Corpuscles.  — 
We  have  seen  that 
white  corpuscles  re- 
semble amoebas  in  their  structure  and  activities.  Let  us  now 
study  their  functions  in  the  human  body.  When  one  gets 
a  sliver  of  wood  in  one's  finger  and  leaves  it  there  for  a  time, 
the  finger  becomes  more  or  less  swollen  and  sore,  and  white 
pus  or  "matter"  usually  forms  in  the  region  of  the  wound. 
All  these  effects  are  probably  due  to  the  presence  of  bacteria, 
which  were  carried  into  the  wound  on  the  piece  of  wood. 
Finding  in  the  tissues  favorable  conditions  for  growth,  these 


w*ss|5«? 


FIG.  43.  —  Human  Blood  Corpuscles. 

Magnified  about  200  times.  Photographed 
through  the  microscope.  The  circular 
disks  are  the  red  corpuscles.  Near  the 
bottom  of  the  photograph  is  a  single 
white  corpuscle  of  larger  size. 


A  STUDY   OF  THE   BLOOD 


123 


minute    organisms   multiply  rapidly  and   produce  poisons 
called  tox'ins,  that  cause  the  inflammation. 

As  soon,  however,  as  these  inflammatory  processes  begin, 
great  armies  of  white  cor- 
puscles are  hurried  to  the 
spot  and  proceed  to  attack 
the  invading  bacteria.  If 
the 


FIG.  44.  -  White  Corpuscles. 


number  of  germs  is 
relatively  small,  and  if  the 
corpuscles  are  in  a  healthy 
condition,  the  latter  seize 
upon  and  devour  the  bac- 
teria in  the  same  way  that  a  =  a  white  corpuscle  devouring  a  bac- 
an  amoeba  takes  in  its  food.  terium. 

Under  these  conditions  lit-    &  =  a  white  corpuscle  destroyed  by  bac- 

tie  if  any  pus   is  formed. 

But  if  the  bacteria  get  the  upper  hand  in  the  struggle,  many 
of  the  corpuscles  are  killed,  and  it  is  the  dead  white  cor- 
puscles that  form  the  pus. 

Amount  of  Blood  in  the  Body — Blood  constitutes  about  one 
thirteenth  of  the  weight  of  the  body;  hence,  in  an  adult 
weighing  one  hundred  and  fifty  pounds  there  would  be  a 
little  less  than  twelve  pounds  of  this  tissue.  Ordinarily  the 
blood  is  distributed  about  as  follows :  — 

one  fourth  in  the  heart,  lungs,  large  arteries,  and  veins, 
one  fourth  in  the  liver, 

one  fourth  in  the  muscles  attached  to  the  skeleton, 
one  fourth  in  the  other  organs  of  the  body. 

4.   THE  HYGIENE  OF  THE  BLOOD 

Conditions  Affecting  the  Red  Corpuscles.  —  Since  supplying 
oxygen  to  the  various  tissues  is  the  function  of  the  red 
corpuscles,  it .  is  very  important  that  their  number  be  suffi- 
cient and  that  they  be  kept  in  a  healthy  condition.  To  this 
end,  an  abundance  of  sleep,  exercise,  fresh  air,  and  nutritious 


124  STUDIES  IN  PHYSIOLOGY 

foods  are  the  essential  conditions.  Every  one  is  familiar  with 
the  fact  that  the  face  looks  pale  after  loss  of  sleep,  or 
when  food  and  fresh  air  are  insufficient,  or  during  periods 
of  physical  inactivity,  and  this  appearance  indicates  a  lack 
of  red  corpuscles.  Habitual  paleness,  or  a-nai'mi-a,  is  a 
disease  requiring  medical  treatment.  It  is  frequently  due  to 
a  want  of  iron  in  the  system ;  hence,  the  efficacy  of  tonics 
containing  this  element.  Fresh  air,  a  moderate  amount  of 
exercise,  and  good  food  are  usually  the  best  remedies  for 
ansemia.  A  good  complexion  is,  therefore,  very  largely 
dependent  on  healthy  blood.  Paint,  powder,  and  other 
cosmetics  will  not  give  such  a  complexion ;  and  besides 
cheapening  the  individual  who  uses  them  habitually,  they 
are  often  a  source  of  permanent  injury  to  the  skin  and 
blood. 

Conditions  affecting  the  Serum All  the  nutrition  of  the 

tissues  is  derived  from  the  blood,  and  all  the  nutrients  of 
the  blood  come  from  the  foods  we  eat.  If  these  foods  are 
insufficient  or  of  an  improper  kind,  the  serum  will  of  course 
be  deprived  of  necessary  ingredients,  and  the  organs  must 
inevitably  suffer  in  consequence.  Hunger  and  thirst  are  the 
sensations  that  tell  us  the  blood  is  in  need  of  new  material 
(see  p.  294).  That  this  is  true  is  proven  conclusively  by  the 
fact  that  these  sensations  disappear  when  water  and  liquid 
food,  instead  of  being  swallowed,  are  injected  directly 
through  the  skin  into  the  blood  vessels.  In  supplying 
material  for  the  blood,  however,  one  must  not  follow  en- 
tirely the  dictates  of  taste.  For  instance,  if  one  is  very 
thirsty,  one  is  tempted  to  drink  rapidly  a  great  quantity 
of  ice-cold  liquid,  when  a  smaller  quantity  of  water,  in 
passing  slowly  through  the  mouth,  will  alleviate  the  thirst 
much  sooner  and  more  completely.  The  importance  of  eat- 
ing proteid  foods  cannot  be  emphasized  too  often.  Healthy 
blood  should  contain  8  %  to  9  %  of  this  kind  of  nutrient, 
and  its  place  can  never  be  filled  by  the  sometimes  more 
palatable  sugars,  starches,  or  fats. 


A  STUDY  OF  THE  BLOOD 


125 


*&£& 

i't&t 


5.   A  COMPARATIVE  STUDY  OF  BLOOD 

Animals  without  Blood.  —  Anioebas  and  other  single-celled 
animals,  as  we  have  seen,  have  no  blood.  In  the  sponges, 
sea  anemones,  and  jellyfishes,  also,  there  is  no  distinct  tissue 
that  can  be  called  blood,  since  absorption  of  food,  respira- 
tion, and  excretion  can  be  carried  on  throughout  the  whole 
of  the  interior  surface  of  these  animals.  All  the  other 
groups  of  animals  have 
some  kind  of  a  circula- 

Color  of  the  Blood.  — 

Many  of  the  inverte- 
brates (animals  having 
no  backbone)  have  color- 
less blood.  There  are, 
however,  exceptions  to 
the  rule.  In  lobsters  and 
other  so-called  "  shell- 
fish," for  example,  blood 
is  bluish,  while  in  worms 
it  is  reddish,  yellowish, 
or  greenish.  In  nearly 
every  vertebrate  the 
blood  is  red. 

Temperature  of  the 
Blood.  —  The  body  tem- 
perature of  a  human  being  in  health  is  981°  Fahrenheit,  and 
this  is  of  course  the  temperature  of  the  blood.  In  fever  this 
sometimes  rises  to  105°  or  even  109°;  in  other  diseases  the 
temperature  may  decrease  a  degree  or  more,  but  any  greater 
variations  from  the  normal  are  usually  fatal.  In  birds  the 
blood  is  about  ten  degrees  warmer  than  it  is  in  man  (i.e. 
108°  F.).  Keptiles  (snakes,  turtles,  and  alligators),  am- 
phibia (that  is,  animals  living  the  first  part  of  their  life  in 
water  and  the  adult  period  on  land,  for  example,  frogs  and 


Fi«.  45.  —  Corpuscles  of  Frog's  Blood. 
Magnified  about  50  times.  Photographed 
through  a  microscope.  The  oval  disks 
with  the  dark  nuclei  are  the  red  corpus- 
cles. In  the  center  are  the  nuclei  of  two 
white  corpuscles  of  smaller  size. 


126 


STUDIES  IN  PHYSIOLOGY 


toads),  and  fishes  are  called  cold-blooded  animals.  In  re- 
ality these  animals  have  the  same  temperature  as  their  sur- 
roundings, and  since  these  surroundings  are  usually  cooler 
than  the  981°  of  man,  these  animals  feel  cold  to  the  touch. 
White  Corpuscles — Even  in  colorless  blood  there  are  cells 
corresponding  to  the  white  corpuscles  of  man  which  have 
the  power  of  altering  their  form  by  amoeboid  movement. 


FIQ.  46.  —A  Comparison  of  Red  Corpuscles. 

We  may,  then,  regard  white  corpuscles  as  a  constant  con- 
stituent of  blood  in  all  animals. 

Red  Corpuscles.  —  Ked  corpuscles  are  found  in  nearly  all 
vertebrates  and  in  vertebrates  only;  but  in  the  various  groups 
there  are  striking  differences  in  their  form  and  size.  Fishes, 
amphibia,  reptiles,  and  birds  usually  have  oval  red  corpus- 
cles which  always  have  a  nucleus.  In  man  and  other 
mammals  no  nucleus  is  seen  in  completely  formed  corpus- 
cles, although  the  cells  in  the  red  marrow  of  bones  from 
which  they  are  formed  do  have  a  nucleus.  All  mammals 


A   STUDY  OF  THE   BLOOD 


127 


have  circular  red  disks,  with  the  exception  of  the  camel 
family,  in  which  they  are  oval.  In  a  given  species  of  ani- 
mals the  diameter  of  red  corpuscles  is  pretty  constant,  but 
one  finds  great  variations  in  size  in  a  comparative  study.  A 
kind  of  amphibian  (Proteus)  has  the  largest  known  corpus- 
cles; the  smallest  are  found  in  the  musk  deer.  Among 
birds  the  size  is  proportional  to  the  size  of  the  animal,  being 
largest  in  the  ostrich  and  smallest  in  the  humming  bird. 

In  murder  trials  a  practical  use  is  made  of  these  striking 
differences  in  red  blood  corpuscles.  If  blood  stains  are  found 
on  an  implement  or  an  article  of  clothing,  microscopical  ex- 
amination can  sometimes  decide  to  what  animal  the  corpus- 
cles belong,  and  in  many  cases  this  evidence  decides  whether 
there  shall  be  conviction  or  acquittal  of  the  accused. 

6.   CHEMICAL  COMPOSITION  OF  BLOOD 
A.    Solid  ingredients. 


1.  Red  corpuscles,  composed  of  — 

a.  Water,  50%. 

b.  Hemoglobin,  over  35%. 

c.  Mineral  matter,  etc.,  5%. 

2.  White  corpuscles,  composed  of 

a.  Water. 

b.  Proteids. 

c.  Mineral  matter. 

B.   Liquid  ingredient  ==  blood  plasma,  composed 

of  — 
1.   Fibrinogen,    which    changes    to    fibrin, 


Forming 

the 
Blood 
Clot. 


2.   Blood  serum,  composed  of 

a.  Water,  about  90%      < 

b.  Proteids,  about  8%  to 


Absorbed 

from 

Alimentary 
Canal.  * 


c.  Fats,  sugars,  and  mineral  matters, 

from  2%  to  1%    < — 

d.  Urea  and  water,  wastes  obtained  from  tissues 

and  carried  to  excretory  organs. 


128  STUDIES  IN  PHYSIOLOGY 

C.   Gaseous  ingredients  (combined  with  other  ingredients  of 
blood). 

1.  Oxygen,  obtained  in  the  lungs  and  carried  to  the 

tissues  by  the  hemoglobin  of  the  red  corpuscles. 

2.  Carbon  dioxid,  obtained  from  the  tissues  and  carried 

by  the  blood  plasma  to  the  lungs,  where  it  is 
excreted. 


CHAPTER   VIII 
A  STUDY  OF  THE  CIRCULATION  OF  BLOOD 

Definition  of  the  Circulation —  We  have  seen  in  the  pre- 
ceding pages  that  the  blood  takes  up  oxygen  in  the  lungs, 
that  it  absorbs  food  materials  while  coursing  through  the 
villi  of  the  intestines,  and  that  it  loses  waste  materials  in 
the  excretory  organs.  It  is  evident,  therefore,  that  this 
important  liquid  must  be  kept  moving  from  one  organ  to 
another.  By  the  term  circulation  of  the  blood  is  meant  the 
ceaseless  movement  of  the  blood  through  a  system  of  tubes 
called  blood  vessels. 

Organs  of  Circulation.  —  The  force  that  drives  the  blood 
around  through  the  body  is  furnished  by  the  contraction  of 
the  muscular  walls  of  the  heart.  Any  blood  vessel  that 
carries  blood  away  from  the  heart  is  called  an  ar'te-ry  (Greek 
aer  =  air  -+-  terein  =  to  hold,  —  a  name  which  was  given  by 
the  early  anatomists  to  those  tubes  because  they  were  found 
empty  after  death,  and  were  therefore  supposed  to  carry 
air).  TJie  veins  are  the  blood  vessels  that  bring  the  blood  back 
to  the  heart.  Connecting  the  arteries  and  the  veins  in  every 
part  of  the  body  are  countless  microscopic  blood  vessels  called 
cap'il-lar-ies  (Latin  eapi#tt*=hair,  so  called  from  their  minute 
size). 

1.   THE  HEART1 

Position,  Shape,  Size.  —  If  any  one  closes  upon  the  palm 
the  fingers  of  his  right  hand  and  places  his  fist  in  the  middle 
of  his  chest  in  such  a  way  that  his  thumb  points  obliquely 

1  See  "Laboratory  Exercises,"  No.  27. 
K  129 


130 


STUDIES  IN  PHYSIOLOGY 


P.K 


downward  toward  the  left  side,  the  fist  will  represent  ap- 
proximately the  size,  shape,  and  position  of  the  heart.  To 
be  more  exact,  one  may  describe  the  heart  of  an  adult  as 

a  conical  organ, 
IX*.  five  inches  in 
length.  It  lies 
diagonally  be- 
hind the  breast- 
bone, near  the 
middle  of  the 
chest  cavity, 
with  its  pointed 
end  or  apex  ex- 
tending toward 
the  left  side  be- 
tween the  fifth 
and  sixth  ribs. 
Since  the  beat 
of  the  heart  is 
felt  most  plainly 
near  the  apex, 
it  is  commonly 
but  erroneously 
believed  that 
the  heart  lies 
on  the  left  side 
of  the  body. 
Let  one  imagine 
the  front  wall 
of  the  chest  cav- 
ity to  be  re- 
moved; one 


FIG.  47.  —  Ventral  View  of  Heart,  Large  Blood  Ves- 
sels and  lungs. 

Ao  =  aorta  curving  toward  left. 
B  =  bronchi  to  lungs. 
(7=  carotid  arteries. 
L.A.  =  left  auricle. 
L.J.V.  =  left  jugular  vein. 
L.L  =  left  lung. 
L.  V=  left  ventricle. 

P.  A  =  pulmonary  artery  dividing  into  two. 
P.  V=  pulmonary  veins. 
R.A  =  right  auricle. 
R.J.V=  right  jugular  vein. 
R.L  =  right  lung. 
R.  V—  right  ventricle. 
S.C.  =  arteries  and  veins  supplying  shoulders  and 

arms. 

T  —  trachea  or  windpipe. 
V.l  =  inferior  vena  cava. 
V.S  =  superior  vena  cava. 


would  then  see 
the  soft,  pink  lungs  on  either  side,  nearly  filling  the  chest 
cavity,  and  between  them  the  heart  (see  Figs.  4  and  47). 
The  Pericardium.  — The  heart  is  not  only  surrounded  by  the 


A   STUDY   OF   THE   CIRCULATION  OF  BLOOD       131 

skeleton  and  muscles  of  the  chest  wall  and  by  the  lungs, 
but  it  is  also  inclosed  in  a  tough  bag  of  connective  tissue 
called  the  per-i-car'di-um  (Greek  peri  =  around  +  cardia  = 
heart).  This  sac  is  attached  to  the  heart  only  at  its  upper 
or  larger  end.  In  size  it  is  considerably  larger  than  the  organ 
it  surrounds,  and  hence  the  heart  has  plenty  of  room  in 
which  to  expand  and  contract  unhindered.  The  inner  layer 
of  the  pericardium  and  a  thin  outer  layer  of  the  heart  (which 
is  continuous  with  the  pericardium)  are  both  formed  of 
smooth,  glistening  se'rous  membrane,  which  secretes  just 
enough  liquid  to  allow  the  heart  to  move  freely  within  its 
case. 

The  Heart  a  Double  Organ. — When  one  makes  a  dissection 
of  the  heart,  one  finds  it  to  be  composed  of  two  halves  which 
are  completely  separated  from  each  other  by  a  muscular  par- 
tition. It  will  help  a  great  deal  toward  understanding  the 
circulation  of  the  blood  if  this  fact  is  kept  constantly  in 
mind,  and  hereafter  the  two  halves  of  the  heart  will  be 
referred  to  respectively  as  the  right  heart  and  the  left  heart. 

The  Cavities  of  the  Right  and  Left  Hearts. — Each  heart  is 
divided  by  a  movable  partition  into  an  upper  and  smaller 
chamber,  called  the  au'ri-de,  and  a  lower  chamber  called 
the  ven'tri-de  (see  Figs.  47,  48,  49).  An  examination  of  the 
outside  of  the  heart  shows  the  significance  of  these  terms ; 
for,  at  the  upper  or  larger  end  are  the  two  small  ear-shaped 
auricles  (Latin  auris  =  ear  -|-  cula  =  little),  while  at  the  apex 
are  the  ventricles  which,  taken  together,  doubtless  reminded 
the  early  anatomists  of  a  small  stomach  (Latin  venter  = 
stomach  +  culus  —  little). 

A  comparison  of  these  four  chambers  shows  important 
differences.  In  the  first  place,  the  auricles  have  relatively 
thin  walls  as  compared  with  the  ventricles,  and  the  reason 
for  this  is  evident  when  we  see  that  their  function  is  simply 
to  receive  the  blood  from  the  veins  and  to  push  it  downward 
into  the  ventricles.  When  one  compares  the  walls  of  the 
left  ventricle  with  those  of  the  right,  one  is  struck  with  the 


132  STUDIES  IN  PHYSIOLOGY 

great  thickness  of  the  former.  The  left  ventricle  does  much 
more  work  than  the  right ;  it  forces  blood  to  the  top  of 
the  head,  to  the  tips  of  the  fingers  and  toes,  and  to  every 
other  organ  of  the  body.  The  right  ventricle,  on  the  other 
hand,  pumps  blood  only  to  the  lungs. 

The  Valves  of  thie  Right  and  Left  Hearts. — We  have  described 
the  partition  between  the  auricles  and  ventricles  as  mov- 
able. In  the  right  heart  there  are  three  triangular  flaps  of 
connective  tissue,  attached  to  the  sides  of  the  opening  from 


FIG.  48.  —  Right  Heart  (opened) .  FIG.  49.  —  Left  Heart  (opened) . 

auricle  to  ventricle.  This  is  the  so-called  tri-cus'pid  valve 
(Latin  tri=  three  +  cuspis  =  point).  When  the  ventricle  is 
empty,  these  flaps  tang  downward ;  but  as  the  blood  pours 
in  from  the  auricle,  their  free  edges  gradually  float  upward 
until,  when  the  ventricle  is  full,  the  three  portions  come 
to  lie  horizontally.  It  is  evident  that  when  the  ventricle 
begins  to  contract,  the  blood  would  tend  to  push  this  valve 
upward  still  further,  thus  allowing  the  blood  to  return 
to  the  auricle.  This  is  prevented,  however,  by  a  number  of 
strong  cords  of  connective  tissue  (the  chor'dce  ten-din' e-ce), 
that  are  attached  at  one  end  near  the  movable  edge  of  the 


A  STUDY  OF  THE  CIRCULATION  OF  BLOOD   133 

valve  flaps,  and  at  the  other  to  muscular  elevations  (the 
pap'iUa-ry  muscles)  on  the  inner  walls  of  the  ventricle.  The 
length  of  the  cords  is  regulated  by  these  muscular  papillae  in 
such  a  way  that  in  a  healthy  heart  the  valves,  when  closed, 
do  not  allow  a  drop  of  blood  to  return  to  the  auricle.  In 
certain  kinds  of  heart  disease  these  flaps  do  not  act  prop- 
erly, and  then  the  skilled  ear  of  the  physician,  listening  at 
the  wall  of  the  chest,  can  detect  at  each  heart  beat  the 
"  murmur  "  caused  by  the  backward  rush  of  the  blood. 

The  valve  in  the  left  heart  works  on  the  same  principle 
as  the  tricuspid  valve  we  have  just  described.  It  consists, 
however,  of  but  two  flaps.  From  its  fancied  resemblance  to 
a  bishop's  mitre  it  has  received  the  name  ml'tral  valve. 

The  Blood  Vessels  connected  with  the  Right  Heart.  —  The 
function  of  the  right  heart,  as  we  have  already  suggested,  is 
that  of  pumping  the  blood,  received  from  the  various  organs 
of  the  body,  to  the  lungs.  Connected  with  the  right  auricle 
'are  two  large  blood  vessels ;  one  brings  in  the  blood  from  the 
organs  in  the  lower  part  of  the  body  (liver,  stomach  intes- 
tines, kidneys,  feet),  and  is  called  the  in-fe'ri-or  ve'na  ca'va 
(Latin  inferior  =  lower  -f  cava  =  hollow  +  vena  =  vein)  ;  the 
other,  the  su-pe'ri-or  ve'na  ca'va,  pours  into  the  right  auricle 
the  blood  from  the  head,  the  arms,  and  the  upper  part  of  the 
trunk.  All  this  blood  is  a  dark  red  or  purplish  color,  because 
it  has  given  up  its  oxygen  to  the  various  tissues  from  which 
it  has  come.  It  must  therefore  load  up  with  oxygen  be- 
fore it  can  again  supply  this  ever  needed  element.  The  new 
supply  of  oxygen  is  secured  in  the  lungs. 

From  the  right  auricle  the  blood  first  goes  into  the  right 
ventricle ;  then  it  is  forced  into  a  large  blood  vessel  called 
the  pul'mo-na-ry  artery  (Latin  pulmonarius,  referring  to  the 
lung).  Soon  after  leaving  the  heart  the  pulmonary  artery 
divides,  giving  off  a  branch  to  each  lung  (see  Figs.  47—49). 

The  Semilunar  Valves. — The  pulmonary  artery  is  always 
full  of  blood,  and  when  the  ventricle  contracts,  this  blood  ves- 
sel has  to  be  stretched  in  order  to  accommodate  the  additional 


134  STUDIES   IN  PHYSIOLOGY 

blood  that  is  forced  into  it.  Hence,  when  the  ventricle  begins 
to  relax,  the  blood  tends  to  rush  back  into  this  chamber  from 
the  pulmonary  artery.  To  prevent  this  three  sem-i-lu'nar 
valves  (Latin  semi  ==  half  -f  luna  =  moon)  are  placed  at  the 
opening  of  the  artery.  Each  valve  is  shaped  like  a  watch 
pocket.  The  three  open  outward  from  the  heart,  but  as  soon 
as  the  ventricle  begins  to  relax,  the  blood  fills  up  the  pockets, 
and  the  three  valves,  by  meeting  in  the  middle  of  the  artery, 
keep  the  blood  from  returning  to  the  ventricle  (Figs.  49  and 
50). 

The  Blood  Vessels  connected  with  the  Left  Heart. — :  After 
receiving  oxygen  in  the  lungs,  the  scarlet  blood  is  brought  to 
the  left  auricle  by  four  pulmonary  veins  (Fig.  49).  It  is  then 
forced  into  the  left  ventricle  and  out  into  the  a-or'ta,  which  is 
the  largest  artery  of  the  body.  Branches  of  this  aorta  supply 
blood  to  every  part  of  the  body  from  the  crown  of  the  head 
to  the  tips  of  the  toes  (Fig.  56).  At  the  opening  of  the  aorta 
are  three  semilunar  valves,  which  work  just  like  those  in 
the  right  heart. 

The  Beat  of  the  Heart. — If  one  etherizes  a  frog,  and  then 
opens  the  chest  cavity,  one  can  watch  the  regular  beating 
of  the  heart.  First  the  two  auricles  contract  at  the  same 
time,  becoming  paler  in  color,  thus  showing  that  the  blood 
has  been  forced  down  into  the  ventricle.  As  soon  as  the 
auricles  have  ceased  to  contract,  the  apex  of  the  heart  (con- 
taining the  ventricle)  begins  its  work,  driving  the  blood  out 
into  the  pulmonary  artery  and  the  aorta.  Meanwhile,  the 
auricles  have  been  relaxing  and  filling  with  blood.  When  the 
ventricle  has  emptied  itself  of  blood,  it  also  relaxes.  If  one 
feels  of  the  heart  at  this  time,  it  is  found  to  be  soft  and 
flabby,  while  during  contraction  it  is  hard. 

The  action  of  the  human  heart  is  much  like  that  described 
for  the  frog.  Each  heart  beat,  therefore,  consists  of  a  contrac- 
tion of  the  two  auricles,  followed  by  a  contraction  of  the  ventri- 
cles; then  comes  the  relaxation  of  the  muscular  walls  and  a 
pause ,  in  which  the  chambers  arejilled  with  blood. 


A  STUDY  OF  THE  CIRCULATION  OF  BLOOD   135 


The  Action  of  the  Valves  of  the  Heart. — Let  us  now  review 
in  succession  the  events  that  occur  within  the  chambers  of 
the  heart  from  the  beginning  of  one  heart  beat  to  the  begin- 
ning of  the  next.  The  walls  of  the  auricles  begin  their  con- 
traction in  the  region  where  the  veins  are  bringing  in  the 
blood.  In  this  way  the  blood  is  prevented  from  being  pushed 
backward,  and  all  of  it  is  forced  into  the  ventricles.  As  long 
as  the  auricles  are  contracting,  the  mitral  and  tricuspid  valves 
are  at  least  partly  open;  but  when  this  contraction  ceases, 
these  valves  are 
forced  by  the  ji 

blood  in  the  ven- 
tricles  into  a 
horizontal  posi- 
tion, but  are 
prevented  from 
going  farther  by 
the  chordae  ten- 
dineae  and  the 
papillary  mus- 
cles. Mean- 
while the  semi- 
lunar  valves  are 
kept  closed  by 
the  pressure  of  the  blood  in  the  aorta  and  pulmonary  artery, 
and  for  an  instant  the  blood  is  held  fast  in  the  grip  of  the 
ventricles. 

The  contraction  of  the  ventricles  now  begins,  and  the 
pressure  on  the  two  sets  of  valves  increases.  The  mitral 
and  tricuspid  valves,  that  close  the  passage  back  to  the  auri- 
cles, cannot  open,  and  so  the  semilunar  valves  are  forced 
back,  and  the  ventricles  drive  on  the  blood  they  have  held 
into  the  two  large  arteries  (pulmonary  and  aorta)  already 
mentioned. 

During  the  contraction  of  the  ventricles  the  auricles  have 
been  relaxing  and  filling  with  blood.  When  the  ventricles 


A  B 

FIG.  50.  —  Diagrams  to  show  the  Action  of  the  Valves 
of  the  Heart. 

A  =  position  of  valves  during  pause. 
B  =  position  of  valves  during  the  contraction  of  the 
ventricle. 


136  STUDIES   IN  PHYSIOLOGY 

relax,  the  semilunars  close,  the  mitral  and  tricuspid  valves 
open,  and  the  blood  passes  into  these  lower  cavities.  For  a 
very  short  time,  therefore,  blood  can  flow  freely  from  the 
mouth  of  the  veins,  through  the  auricles,  down  into  the 
ventricles.  But  as  the  latter  fill,  the  valves  float  up  toward 
a  horizontal  position.  Then  comes  the  contraction  of  the 
auricles,  which  begins  the  whole  series  of  events  just  de- 
scribed. 

We  may  summarize  as  follows  what  we  have  learned  in 
regard  to  the  action  of  the  valves  :  (1)  when  the  auricles 
contract,  the  mitral  and  tricuspid  valves  are  open  and  the 
semilunar  valves  are  closed  ;  (2)  when  the  ventricles  con- 
tract, the  semilunar  valves  are  open  and  the  mitral  and 
tricuspid  valves  are  closed  ;  (3)  during  the  pause  before  the 
beginning  of  the  next  heart  beat,  the  mitral  and  tricuspid 
valves  are  open,  and  the  semilunar  valves  are  closed  [as 


Sounds  of  the  Heart.  —  If  one  listens  at  the  chest  wall,  one 
can  hear  two  distinct  sounds  during  each  heart  beat.  The 
*  first  sound  is  longer  and  more  muffled  ;  it  may  be  compared  to 
the  syllable  lub,  and  is  probably  caused  by  the  vibration  of  the 
valve  flaps  and  the  chordae  tendineae  when  the  contraction  of 
the  ventricles  closes  the  mitral  and  tricuspid  valves.  The 
second  sound  is  short  and  sharp,  like  the  syllable  dup.  It 
follows  the  contraction  of  the  ventricles  and  is  due  to  the 
quick  closing  of  the  semilunar  valves  by  the  pressure  of  the 
blood  in  the  arteries. 

The  Blood  Supply  for  the  Heart.  —  One  of  the  hardest  worked 
organs  of  the  whole  body  is  the  heart.  During  every  minute 
of  our  lifetime  it  contracts  from  sixty  to  a  hundred  and 
twenty  times,  and  the  only  time  it  gets  for  rest  is  during 
the  pause  of  a  fraction  of  a  second  after  each  heart  beat. 
The  heart  muscle  must,  therefore,  be  oxidized  to  furnish 
energy  for  all  this  work,  and  consequently  new  building 
material  must  be  continually  furnished.  An  abundance  of 
blood  passes  through  the  cavities  of  the  heart,  but  the  walls 


A  STUDY  OF  THE  CIRCULATION  OF  BLOOD   137 

are  so  thick  that  none  of  it  can  soak  out  into  the  muscle 
even  if  there  were  time  to  do  so.  Just  beyond  the  semilunar 
valves  of  the  aorta,  two  arteries  (the  cor'o-na-ry  arteries) 
are  given  off ;  these  at  once  pass  over  and  through  the  walls 
of  the  right  and  left  hearts  (like  a  crown;  hence,  Latin 
corona  =  crown),  sending  branches  into  every  part  of  the 
working  tissue. 

2.   THE  BLOOD  VESSELS 

Position  of  Arteries  and  the  Pulse. — We  have  defined  an 
artery  as  a  blood  vessel  carrying  blood  from   the   heart. 


A  V 

FIG.  51.  — Cross  Section  of  an  Artery  (A),  and  of  a  Vein  (7). 

c  —  connective  tissue.  m  =  muscle  layers. 

e.c  =  cells  of  serous  lining.  n  =  nuclei  of  serous  cells. 

Every  time  the  ventricles  contract,  we  have  seen  that  the 
aorta  and  pulmonary  artery  are  stretched ;  this  is  true  of 
every  artery  in  the  body.  Most  arteries  lie  beneath  thick 
layers  of  muscle  or  bone,  which  protect  them  from  possible 
injury;  but  in  certain  regions  of  the  body  they  run  close  to 
the  surface.  If  one  places  one's  forefinger  on  the  wrist  of 
one's  other  hand,  just  at  base  of  the  thumb,  one  can  feel  a  dis- 
tinct beating,  called  the  pulse.  This  is  due  to  the  enlarge- 
ment of  the  artery  at  each  heart  beat.  When  an  artery  is 
cut,  therefore,  the  blood  is  forced  out  in  spurts  at  each  con- 
traction of  the  ventricle. 

Structure  of  Arteries. — If  one  cuts  off  a  piece  of  the  aorta 
of  any  animal,  one  finds  that  the  blood  vessel  retains  its 


138 


STUDIES   IN   PHYSIOLOGY 


tubular  form.  It  can  be  stretched  to  a  considerable  extent ; 
but  resumes  its  original  form  and  size  when  the  force  is 
removed.  In  the  cross  section  of  an  artery  one  can  distin- 
guish three  layers.  The  outer  layer  is  formed  of  interlacing 
connective  tissue  fibers.  Beneath  this  covering  is  a  thick 
layer  composed  of  muscular  and  elastic  tissue.  It  is  the 
elastic  tissue  that  allows  the  arteries  to  expand  when  more 
blood  is  forced  into  them  by  the  contraction  of  the  ventricles. 
After  each  pulse  these  elastic  walls  squeeze  the  blood  forward 
into  the  capillaries ;  arteries,  therefore,  are  specially  adapted 

to  keep  the  capillaries  full 
of  blood.  The  third  layer 
forms  a  smooth  lining  for 
the  tube ;  it  is  composed  of 
serous  membrane  (Fig.  51). 
Position  of  the  Veins.  — 
On  the  back  of  the  hand 
one  sees  through  the  skin 
a  branching  system  of  blu- 
ish blood  vessels.  These 
are  veins.  Unlike  the 
arteries,  veins  have  no 


B 
FIG.  52.  —  Valves  in  a  Vein. 


A  =  vein  laid  open  to  show  pouch-shaped 

valves. 
B  —  section  of  vein,  showing  valve  open 

by  flow  of  blood  toward  heart. 
C=  section  of  vein,  showing  valve  closed    pulse,    as    One    can    easily 

by  flow  of   blood  back   toward    ' 

capillaries.  Prove   bJ   pressing    one's 

finger  upon  one  of  them. 

Since  blood  flows  slowly  and  steadily  back  to  the  heart 
through  the  veins,  there  is  little  danger  of  any  consider- 
able loss  of  blood,  even  if  some  of  them  should  be  injured. 
Many  veins  lie  near  the  surface,  while  most  of  the  arteries, 
as  we  have  just  stated,  are  buried  deeply  among  the  other 
tissues. 

The  Structure  of  Veins. — When  the  veins  are  emptied  of 
blood,  they  immediately  collapse.  In  a  cross  section  of  one 
of  these  blood  vessels  (as  in  that  of  an  artery)  can  be  seen 
three  layers,  connective  tissue,  muscular  and  elastic  tissue, 
and  the  serous  lining,  but,  as  would  be  expected,  each  layer 


A  STUDY   OF  THE   CIRCULATION   OF  BLOOD       139 

is  much  thinner  than  is  the  case  in  the  walls  of  an  artery 
(Fig.  51).  Veins,  however,  are  provided  with  valves  shaped 
much  like  the  semilunars  of  the  aorta  and  pulmonary  artery. 
The  blood  can  flow  toward  the  heart,  but  as  soon  as  it  begins 
to  pass  in  the  opposite  direction,  these  valves  are  immedi- 
ately filled  and  thus  the  passage  is  obstructed  (Fig.  52).  If 
one  ties  a  cord  tightly  about  the  wrist,  one  can  see  the  veins 
swell,  and  small  hillocks  appear  which  indicate  the  position 
of  the  valves  just  described. 

Position  of  the  Capillaries. — As  we  trace  the  arteries  far- 
ther and  farther  from  the  heart,  we  see  that  they  divide  and 
subdivide  until  very  small  branches  are  formed.  That  these 
fine  branches  are  still  arteries  is  proved  by  the  fact  that 
elastic  and  muscular  tissue  are  present  in  their  walls.  Fi- 
nally, however,  these  tiny  blood  vessels  become  continuous 
with  still  smaller  tubes,  the  capillaries.  So  numerous  are 
the  capillaries  that  one  cannot  push  the  point  of  a  needle 
for  any  considerable  distance  into  any  organ  of  the  body 
without  piercing  a  number  of  them.  These  smallest  of 
blood  vessels  communicate  freely  with  one  another  and 
form  a  complicated  network  of  tubes  that  bring  blood 
close  to  all  cells  of  the  body.  As  the  capillaries  begin 
where  arteries  end,  so  they  end  where  the  smallest  veins 
begin.  Throughout  the  body,  therefore,  is  a  continuous 
system  of  blood  vessels. 

Importance  of  the  Capillaries.  —  If  the  blood  were  kept  con- 
stantly within  this  system  of  tubes,  it  would  be  entirely  un- 
able to  help  in  the  nutrition  of  the  body.  Each  cell  must 
take  from  the  blood  the  nutrients  it  needs  for  its  special 
work;  likewise  it  must  give  off  to  the  blood  the  wastes  it 
has  formed  by  oxidation.  It  is  through  the  thin-walled 
capillaries  tlrnt  all  these  exchanges  of  materials  occur. 
Hence,  the  capillaries  form  the  most  important  portion,  of 
the  blood  system.  We  may  regard  the  arteries  as  the  sup- 
ply pipes  for  the  capillaries,  and  the  veins  as  the  drain 
pipes  from  them. 


140 


STUDIES  IN  PHYSIOLOGY 


Structure  of  the  Capillaries.  —  In  structure  the  capillaries 
are  extremely  simple.  At  the  points  in  the  blood  system 
where  arteries  end  and  capillaries  begin,  connective,  mus- 
cular, and  elastic  tissues  disappear.  The  walls  of  the  capil- 
laries are  continuous  with  the  inner  lining  of  the  arteries 
and  the  veins,  and  are  formed  of  a  single  layer  of  very  thin 
cells'.  We  have  in  this  arrangement  the  best  possible  con- 
ditions for  the  process  of  osmosis.  Only  the  thin  membrane 
of  ^he  capillary  wall  separates  tLe  blood  from  the  surround- 
ing tissues, 

1  and     an     ex- 

change of  ma- 
terials  be- 
tween the  two 
is  readily  car- 
ried on  (Fig. 
53). 

Flow  of  Blood 
in  the  Web  of 
a  Frog's  Foot.1 
—  One  can 
easily  watch 
the  flow  of  the 
blood  in  the 

thin  web  of  a  frog's  foot.  If  a  1  %  solution  of  chloretone  is 
forced  into  the  mouth  of  the  animal  and  its  body  is  wrapped 
in  a  wet  cloth,  the  frog  will  lie  perfectly  passive,  and  the 
thin  membrane  can  be  spread  out  and  examined  with  the 
microscope.  Under  these  conditions  one  can  trace  the  blood 
current  from  the  arteries  through  the  capillaries,  into  the 
veins,  and  a  most  fascinating  study  it  is.  One  can  see  in  all  of 
the  tubes  a  large  number  of  oval-shaped  red  corpuscles,  and 
possibly  here  and  there  a  more  or  less  spherical  white  corpus- 
cle. These  are  carried  along  in  the  transparent  stream  of 
colorless  plasma.  In  some  of  the  larger  vessels  the  current 
1  See  "Laboratory  Exercises,"  No.  28. 


B  AC 

FIG.  53.  —  Capillaries 

A  =  surface  view.  C—  cross  section. 

B  =  longitudinal  section.         d  =  interior  of  capillary. 
e.c  =  cells  forming  wall  of  capillary. 
n  =  nuclei  of  cells. 


A  STUDY  OF  THE  CIRCULATION  OF  BLOOD   141 

is  driven  forward  in  jerks ;  we,  therefore,  infer  that  we  are 
looking  at  arteries.  As  the  arteries  subdivide  and  become 
smaller,  the  pulse  gradually  disappears,  and  in  the  capil- 
laries there  is  a  steady  stream  on  toward  the  veins.  Some 
of  the  capillaries  are  so  small  that  but  a  single  corpuscle 
can  pass  through  at  a  time; 
indeed,  they  are  sometimes 
squeezed  out  of  shape  within 
the  microscopic  tube,  but  on 
escaping  into  the  larger  blood 
vessels  they  resume  their 
former  shape  (see  Fig.  54). 

Absence  of  Pulse  in  Capillaries 
and  Veins.  —  It  is  clear  that  if 
the  pulse  were  transmitted 
from  the  arteries  to  the  capil- 
laries, the  thin  walls  of  the  FIG.  54.— Capillaries  of  Frog's  Foot, 
latter  would  be  unable  to  with-  The  capillary  tubes  are  more  or  less 
stand  the  pressure;  the  blood  filled  with  the  oval  red  corpuscles, 
would  then  escape  from  the  The  irregular  black  spots  are  the 

pigment  cells  which  give  color  to 
capillaries  and  flood  the  vari-      the  skin  of  the  frog. 

ous  tissues.  Hence,  there  must 

be  some  means  of  reducing  the  pressure  in  the  blood  vessels 

before  the  capillaries  are  reached. 

At  least  two  causes  combine  to  produce  the  even  flow  of 
blood  in  the  capillaries  and  veins.  In  the  first  place,  the 
arteries  near  the  heart  expand  at  every  contraction  of  the 
ventricle,  thus  making  room  for  the  additional  cupful  of  blood 
that  is  forced  out  at  each  heart  beat.  This  expansion  of  the 
arteries,  however,  becomes  less  and  less  as  the  blood  enters 
the  smaller  branches.  In  the  second  place,  if  all  the  fine 
capillaries  of  the  body  could  be  placed  side  by  side,  their 
combined  diameters  would  be  many  times  the  diameter  of  all 
the  arteries  that  supply  them  with  blood.  Hence,  as  the 
blood  is  pushed  outward  from  the  heart,  it  finds  more  and 
more  room  in  which  to  flow.  The  size  of  each  capillary  is 


142  STUDIES   IN  PHYSIOLOGY 

so  small,  however,  that  there  is  a  great  deal  of  friction,  and 
the  blood  is  therefore  obliged  to  move  more  slowly.  These 
two  characteristics  of  structure  explain  the  absence  of  a 
pulse  in  the  capillaries.  When  the  blood  passes  into  the 
veins,  its  current  is  also  slow  and  without  any  pulse. 

3.   THE  CIRCULATION  OF  THE  BLOOD 

Having  completed  our  survey  of  the  structure  and  action 
of  the  heart  and  the  blood  vessels,  we  are  ready  to  study 
the  blood  system  as  a  whole  and  to  learn  how  the  blood  gets 
to,  through,  and  from  every  organ  of  the  body. 

The  Two  So-called  Systems  of  Circulation.  —  In  our  study  of 
the  heart  we  always  referred  to  the  right  and  left  hearts  as 
though  they  were  entirely  apart  from  each  other.  Let  us 
keep  this  distinction  in  mind  in  considering  the  circulation 
of  the  blood,  for  there  are  likewise  two  distinct  systems  of 
blood  vessels.  One  system  carries  the  blood  to,  through, 
and  from  the  lungs;  it  is  for  this  reason  called  the  pulmo- 
nary circulation.  The  other  system  is  known  as  the  sys- 
temic, which  supplies  blood  to  every  other  portion  of  the  body, 
that  is,  to  the  general  system. 

The  Pulmonary  Circulation.  —  In  order  to  understand  the 
pulmonary  circulation  we  need  only  review  the  facts  we 
have  already  learned.  The  blood  is  driven  by  the  contraction 
of  the  right  ventricle  past  the  semilunar  valves  into  the  pul- 
monary artery,  which  soon  branches,  giving  off  an  artery  to 
each  lung.  After  passing  through  the  finer  pulmonary  arter- 
ies and  capillaries,  the  blood  is  finally  collected  by  the -four 
pulmonary  veins,  which  empty  into  the  left  auricle,  whence 
the  blood  comes  into  the  left  ventricle  (see  Fig.  55). 

The  Systemic  Arteries.  —  From  the  left  ventricle  the  blood 
stream  is  forced  into  the  aorta.  This  great  supply  pipe  of 
the  body  first  arches  over  toward  the  left,  like  a  shepherd's 
crook ;  it  then  passes  posteriorly  through  the  dorsal  part  of 
the  chest  cavity  and,  piercing  the  diaphragm,  it  enters  the 
abdomen.  Three  regions  of  the  aorta,  therefore,  can  be 


A  STUDY  OF  THE  CIRCULATION  OF  BLOOD   143 


distinguished:  first  the  arch  of  the  aorta,  second  the  thoracic 
or  chest  aorta,  and  third  the  abdominal  aorta  (Figs.  o£  and  56). 


/  Cff/}///ar/es  of  % 


Mews  from  faatf 


Lymphatics  from-  _ . 
bpper/wrt  of  body 

Opening  of /ymfi/?fft/cs 
/ffto  veins 


Sujoer/or  vena  cai/a-  -  -  — 
Pu/mor/crry  artery — --6 
/?/§/? t  OLi/ricfe  -  - 


/nfer/or  i/er?aca/a  -fj- 
Se/n/'/t/rtan/a/ves  ^ 


lymphatics  from--— 
<ower  part  of  body 


Porta/ i/e/r?   **•    ,\ 
fro/n 


fans  from  fi/&/?eys'  '  ' 
Heris  from  leys 


^  ^Arteries  tofaad 
&/?tf  arrr/s 


,-l.eftaur/cJe 


Arc/?  of  aorta 

-SemJ/urtar  va/ves 
of  aorta 

~  -  -  Chordae  te/?d/rieae 
"--rftorac/c  aorta 

^"-Left  ver?tr/c/e 
—  Cqpiff0s/e$  ofsto/nacf/ 
-  ~/4rter/es  to  stomac/1, 


Ca/}///ar/es  of 
/r/fest//?e 


L— -Art&rtes  to  mtest/ne 

Arteries  to  k/cfneys 

?s  of fadr/eys 


'- — drter/es  fo  teas  and  feet 
* . .  -Ca/y/7/artes  /n/eas  ana" feet 


FIG.  55.  —  Diagram  of  the  Pulmonary  and  Systemic  Circulations. 

Red  color  indicates  blood  rich  in  oxygen.     Blue  color  indicates  blood  poor 
in  oxygen.    Purple  color  indicates  blood  in  capillaries. 

From  the  top  of  the  arch  of  the  aorta  on  the  right  side,  a 
large  trunk  is  given  off,  which  soon  divides  into  two  parts: 
one  branch  (the  right  ca-rot'id  artery)  runs  upward  through 


144  STUDIES  IN  PHYSIOLOGY 

the  neck  region  to  supply  the  right  half  of  the  head;  the 
other  division  passes  under  the  collar  bone,  down  alongside 
the  upper  arm  bone,  and  near  the  elbow  divides  into  the 
ra'di-al  and  ul'nar  arteries,  which  lie  close  to  the  bones  of 
the  forearm,  from  which  they  are  named.  (The  pulse  is 
usually  taken  by  feeling  the  radial  artery.)  From  the  left 
side  of  the  aortic  arch  two  distinct  arteries  are  given  off. 
The  left  carotid  artery  takes  a  course  similar  to  the  right 
carotid  described  above,  thus  supplying  the  left  half  of  the 
head.  The  left  arm,  forearm,  and  hand  are  supplied  by 
a  separate  branch  from  the  left  side  of  the  arch.  The  coro- 
nary branches  from  the  arch  of  the  aorta,  that  run  into  the 
muscle  of  the  heart  itself,  have  been  already  described. 

As  the  aorta  passes  downward  through  the  chest  cavity 
(the  thoracic  aorta),  it  supplies  blood  to  the  air  tubes  and 
lung  tissue  (bronchial  arteries),  to  the  esophagus,  and  to 
the  muscles  that  move  the  ribs  and  the  spinal  column. 

In  the  abdominal  region  five  principal  branches  are  given 
off  from  the  aorta.  The  first  (the  coe'li-ac  axis)  soon  divides 
into  three  parts,  which  supply  the  stomach  (gastric  artery], 
the  spleen  (splenic  artery),  and  the  liver  (hepatic  artery) 
respectively.  Two  other  branches  (the  upper  and  lower 
mes-en-ter'ic  arteries)  carry  blood  to  the  walls  of  the  intes- 
tines. The  two  other  arteries  branch  off  to  the  kidneys 
(renal  arteries).  In  the  posterior  part  of  the  abdominal 
cavity  the  aorta  divides  into  two  trunks,  which  supply  the 
hips,  thighs,  and  lower  legs. 

The  Systemic  Veins.  —  After  passing  through  the  capillaries 
in  each  of  the  organs  we  have  mentioned,  the  blood  returns 
to  the  right  heart  through  the  veins.  In  general  it  may  be 
said  that  the  larger  veins  follow  the  course  of  the  arteries. 
Thus  a  large  vein  (the  jug'u-lar)  carries  blood  downward 
from  the  head  on  either  side  of  the  neck ;  two  others  pass 
upward  along  the  arms  ;  and  these  four  veins  at  length  unite 
to  form  the  superior  vena  cava,  which  empties  the  blood  into 
the  right  auricle.  In  a  similar  way  the  inferior  vena  cava 


A   STUDY   OF   THE   CIRCULATION   OF   BLOOD       145 


Arch  of  aorta\  ^ 


f?/g/7t  ventr/c/e  .  .  . 


/r/ferior  vena  cava 
Ve/rrs  from-  ----- 


crorfa  fo /ntest/nes 

£ras?c/?es  of-" 
aorta  to  fefs 


^  /e/ns  fro/nfreffcf 
'    f jugular  veins) 

•''"     „  -Arteries  fo  heard 
,..-.•'*        fcarofta  arteries 

J/e/n  from  arm 

A/tery  to  arm 

~r/?orac/c  aorta 
\--Stomacr? 

l\  1  I £rar>cf>  ofaorta  to 

-\~1lu         stofr?ach,sp/ee? 


Sp/eer? 

-tfarafict/ artery 
U/r/ar  artery 

"*•  Branches  of  aorta 
to  kiofneys 


— Artery  to  /e$  /ferr/ora/j 
---  few  from  tea 


FIG.  56.  — The  Systemic  Arteries  (red)  and  Veins  (blue). 

brings  to  the  same  auricle  the  blood  from  the  lower  part  of 
the  body.  One  portion  of  this  lower  venous  system,  however, 
requires  special  description. 

The  Portal  System  of  Veins.  —  The  blood  from  the  spleen,  the 
pancreas,  the  stomach,  and  the  intestines  takes  a  somewhat 


146  STUDIES   IN   PHYSIOLOGY 

roundabout  course  back  to  the  heart.  The  veins  from  these 
four  organs  unite  to  form  the  large  portal  vein,  which  enters 
the  liver,  and  there  divides  to  supply  a  system  of  capillaries. 
These  in.  turn  send  the  blood  into  the  he-pat'ic  veins  (Latin 
hepaticus,  referring  to  the  liver),  which  empties  into  the  in- 
ferior vena  cava.  The  peculiarity  of  the  portal  system  lies 
in  the  fact  that  the  blood  supplied  by  the  aorta  to  these  organs 
of  the  abdomen  passes  through  two  sets  of  capillaries  before 
returning  to  the  heart  (see  Figs.  55  and  36).  In  our  study  of 
the  liver  we  learned  that  one  of  its  most  important  functions 
is  that  of  storing  carbohydrate  food  in  the  form  of  glycogen. 
The  portal  system  of  veins  is  an  adaptation  to  this  function, 
for  the  blood  from  the  stomach  and  the  intestines  is  often 
well  supplied  with  sugar  which  may  be  left  for  a  time  in  the 
liver.  Blood  from  the  kidneys,  on  the  other  hand,  has  not 
been  supplied  with  this  nutrient,  and  so  passes  directly  into 
the  inferior  vena  cava. 

The  liver,  it  will  be  remembered,  contains  one  fourth  of 
all  the  blood  in  the  body,  and  this  blood  is  of  two  kinds. 
One  kind  is  furnished  direct  by  a  branch  of  the  aorta  (hepatic 
artery);  the  other  kind  comes  to  the  liver  through  the  portal 
vein.  The  latter  is  the  only  vein  in  the  body  that  supplies 
blood  to  capillaries. 

The  Circulation  but  a  Single  System.  —  To  keep  the  course  of 
the  blood  clearly  in  mind,  we  have  carefully  distinguished 
a  pulmonary  from  a  systemic  circulation.  In  reality,  how- 
ever, there  is  but  a  single  circulation  in  the  body.  The 
blood  cannot  pass  across  from  the  right  heart  to  the  left 
heart.  In  order  to  get  back  to  the  right  ventricle,  for 
instance,  a  drop  of  blood  must  first  go  through  a  system  of 
capillaries  in  the  lungs,  must  return  to  the  left  heart,  and 
must  thence  be  driven  through  a  second  set  of  capillaries 
before  it  reaches  the  point  from  which  it  started.  And  if, 
perchance,  this  drop  of  blood  goes  through  the  tissues  of 
the  stomach  or  intestines,  or,  in  other  words,  through  the 
portal  system,  it  must  pass  through  three  different  sys- 


A   STUDY   OF   THE   CIRCULATION   OF  BLOOD       147 


terns  of  capillaries  before  it  can  begin  a  second  round  of  the 
body. 

Changes  in  the  Composition  of  the  Blood.  — The  composition 
of  the  blood  is  continually  changing  in  its  passage  through 
the  various  tissues  of  the  body.  We  may,  perhaps,  make 
clearer  these  various  changes  by  expressing  them  in  tabular 
form  as  follows  :  — 


In    muscular,    nerve, 
and  other  tissues, 


In  lining   of    mouth, 
stomach,  intestines, 


In  lungs, 

In  kidneys  and  skin, 


BLOOD  LOSES 

Materials  needed  for 
growth,  repair,  and 
production  of  en- 
ergy. 

Materials  needed  for 
the  manufacture  of 
digestive  juices  (and 
for  growth  and  re- 
pair). 

Carbon  dioxid  and 
water. 

"Water  and  urea. 


BLOOD  GAINS 
Wastes  formed  by  me- 
tabolism (carbon  di- 
oxid, water,  urea;. 

Digested  nutrients 
(proteids,  fat, 
starch,  sugar,  min- 
eral matters,  and 
water)  and  wastes. 

Oxygen. 

Carbon  dioxid. 


Inappropriateness  of  the  Terms  "Arterial"  and  "Venous."  — 
Thus  far  we  have  avoided  the  terms  ar-te'ri-at  and  ve'nous  as 
applied  to  blood.  These  terms  are  commonly  used  in  text- 
books, but  they  often  give  rise  to  considerable  confusion. 
By  arterial  blood  is  meant  the  bright  scarlet  blood  that 
comes  back  from  the  lungs  to  the  left  heart,  whence  it  is 
distributed  through  the  aorta  to  all  parts  of  the  body.  The 
word  arterial,  however,  suggests  arteries,  and  orie  easily 
jumps  at  the  conclusion  that  arterial  blood  is  always  car- 
ried in  arteries.  This  is  not  true ;  the  pulmonary  artery 
carries  the  dark  colored  or  so-called  venous  blood.  In  the 
same  way  venous  blood  is  commonly  supposed  to  flow  only  in 
veins ;  but  we  must  bear  in  mind  that  the  pulmonary  veins 
carry  arterial  blood.  The  difference  in  the  color  of  the 
blood  is  due  almost  entirely  to  the  amount  of  oxygen  that 
is  present.  Hence,  we  may  avoid  all  possible  confusion  by 
calling  the  bright  scarlet  blood  ox'y-gen-a-ted  blood,  or  blood 


148  STUDIES  IN  PHYSIOLOGY 

rich  in  oxygen ;  while  the  darker  blood  may  be  described  as 
de-ox'y-gen-a'ted  blood.  The  former  is  not  necessarily  pure 
blood,  nor  is  the  latter  always  impure.  The  purest  blood 
of  the  body  is  undoubtedly  the  dark  colored  blood  that 
pours  into  the  inferior  vena  cava  from  the  kidneys,  for 
when  it  reaches  the  kidneys  it  has  already  lost  in  the  lungs 
its  carbon  dioxid;  in  the  kidneys  the  water  and  urea  are 
removed. 

Regulation  of  the  Blood  Supply  to  the  Various  Organs.  —  Every 
one  knows  that  the  pulse  beat  is  more  rapid  and  the  body 
feels  warmer  during  vigorous  exercise.  The  feeling  of  warmth 
is  due  to  the  more  rapid  metabolism  that  is  going  on  in  the 
muscles,  and  because  of  this  metabolism  there  is  need  of 
a  greater  supply  of  blood  to  repair  the  wasting  tissues. 
Since  there  is  seldom  more  than  twelve  pounds  of  blood 
in  the  body  of  an  adult,  other  organs  must  do  without 
their  usual  supply  if  the  working  muscles  are  to  receive 
the  amount  of  blood  that  they  need.  It  will  be  remembered 
that  in  the  description  of  the  arteries,  the  presence  of  muscle 
tissue  was  noted ;  it  is  these  muscles  in  each  artery  that  de- 
termine its  size.  When  a  considerable  amount  of  blood  is 
needed,  for  instance,  in  the  brain,  the  muscles  of  the  arteries 
in  this  part  of  the  body  relax,  and  the  vessels  become  larger. 
In  other  parts  of  the  body,  however,  there  must  be  at  the  same 
time  a  corresponding  decrease  in  the  size  of  arteries  by  the 
contraction  of  the  circular  muscles.  All  these  changes  in 
the  diameter  of  arteries  are  regulated  by  the  sympathetic 
nervous  system. 

4.   THE  LYMPHATIC  SYSTEM 

The  Lymph.  — From  our  discussion  of  the  structure  and 
use  of  the  capillaries,  one  might  infer  that  the  liquid  nutri- 
ents of  the  blood  pass  directly  from  these  thin-walled  tubes 
into  the  tissue  cells,  and  that  waste  substances  are  given  off 
from  the  cells  directly  to  the  blood.  In  reality  this  is  not 
true.  In  the  tissues  of  the  body  there  are  countless  small 


A  STUDY  OF  THE  CIRCULATION  OF  BLOOD   149 


spaces,  and  as  the  blood  passes  through  the  capillaries,  part 
of  the  plasma  soaks  out  by  osmosis  and  keeps  these  spaces 
filled  with  a  watery  liquid  known  as  the  lymph  (Latin 
lymplia= water).  Occasionally  the  colorless  corpuscles  work 
their  way  by  amoeboid  motion  out  between  the  cells  of  the 
capillary  wall,  and  so  escape  into  the  lymph. 
One  might,  therefore,  say  that  the  tissues 
are  bathed  with  lymph,  which  is  really  blood 
minus  the  red  corpuscles,  and  considerably 
diluted  ivith  water. 

Changes  in  the  Lymph.  —  Since  this  liquid 
is  in  immediate  contact  with  the  tissues,  the 
cells  can  take  from  it  the  nutrients  necessary 
for  their  growth  and  repair,  and  at  the  same 
time  can  unload  into  the  lymph  their  use- 
less burden  of  waste  matters.  The  lymph 
in  turn  gives  off  some  of  these  waste  materi- 
als to  the  blood  and  receives  new  supplies 
of  nutritive  ingredients.  In  this  way  the 
lymph  acts  as  a  middleman  between  the  blood 
and  the  tissues.  By  this  constant  inter- 
change of  materials  the  lymph  in  a  given 
organ  is  kept  tolerably  constant  in  its  com- 
position, but  in  different  organs  this  liquid 
varies  considerably. 

The  Lymphatics.  —  The  amount  of  lymph 
is  constantly  increased  by  the  osmosis  that 
goes  on  in  the  capillaries.  Hence,  if  there 
were  no  provision  for  draining  lymph  back 
into  the  blood  system,  the  tissues  would  become  unduly  dis- 
tended. Such  is  the  case  in  the  condition  known  as  dropsy. 
This  drainage  is  accomplished  by  a  system  of  vessels  known 
as  the  lym-phat'ics.  The  lymphatics  begin  as  extremely  mi- 
nute, thin-walled  tubes,  which  open  freely  from  the  spaces 
between  the  cells.  As  the  tubes  pass  out  through  the  tissues, 
they  unite  to  form  larger  vessels  (see  Fig.  57),  and  these 


FIG.  57.  —  Lym- 
phatics of  the 
Right  Arm. 


g 


lymphatic 
nodes. 


150 


STUDIES  IN  PHYSIOLOGY 


finally  enter  a  duct  of  considerable  size  (the  tho-rac'ic  duct) 

which  carries  the  lymph 
up  ward -from  the  abdomi- 
-/  nal  cavity,  through  the 
chest  or  thoracic  cavity 
(see  Fig.  58,  a,  6).  The 
thoracic  duct  finally  emp- 
ties the  lymph  into  a 
branch  of  the  superior 
vena  cava  on  the- left  side 
of  the  neck  (Fig.  58,/), 
and  in  this  way  the  liquid 
that  has  soaked  out  from 
the  blood  is  restored  to 
the  circulation.  A  smaller 
duct  drains  off  portions 
of  the  right  side  of  the 
trunk  into  a  right  branch 
of  the  superior  vena  cava 
(Fig.  58,  7i),  and  at  vari- 
ous other  points  in  the 
body  lymphatics  empty 
into  blood  vessels. 

Throughout  the  course 
of  the  lymphatics  are 
found  valves  much  like 
those  in  the  veins  (Fig. 
59).  These  prevent  the 
FIG.  58. -The  Thoracic  Duct.  lymph  from  taking  a 

a,b  =  thoracic  duct.  backward  course.    Small 

c  =  opening  of  duct  into  veins.  swellings      (lymphatic 

d—  lymphatic  nodes  in  lumbar  re-  7    N          •,••>  ~         -, 

gion.  nodes)  are  likewise  found 

f, g, h  =  superior    vena    cava    and     its     at     frequent     intervals 

branches.  /T7,.        ~~x       mi 

1  =  part  of  rib.  (Flg-  59);      Their  Prmcl' 

pal  function  is  supposed 
to  be  that  of  forming  new  white  corpuscles.     They  also 


A   STUDY  OF  THE   CIRCULATION   OF  BLOOD       151 


probably  serve  as  filters  in  which  disease  germs  and  other 
foreign  bodies  are  removed  from  the 
lymph  and  destroyed. 

The  Lacteals.  —  One  portion  of  the 
lymphatic  system  has  been  already 
referred  to  in  our  study  of  the  villi 
of  the  small  intestines  (see  p.  95). 
The  lacteals  were  described  as  small 
tubes  in  the  center  of  each  villus 
(Fig.  35).  They  are,  however,  larger 
than  the  lymphatic  in  other  parts  of 
the  body.  The  fat  which  is  absorbed 
by  these  lacteals  is  poured  with  the 
rest  of  the  lymph  into  the  thoracic 
duct,  and  by  this  indirect  course 
reaches  the  blood  that  enters  the 
right  auricle.  Unlike  the  other  mi-  FlG  59  _A  Lymphatic 
trients,  therefore,  the  fat  does  not  Node,  showing  Lym- 

pass  through  the  liver  on  its  way  to     Phati?s    (wjth   Valves) 

entering  and  leaving  the 
the  heart.  Node. 


5.   HYGIENE  OF  THE  CIRCULATORY  SYSTEM 

Effect  of  Heat  and  Cold  on  the  Arteries.  —  It  is  a  fact  of 
common  experience  that,  when  the  hands  or  other  parts  of 
the  body  are  plunged  into  hot  water,  they  assume  a  bright 
red  color.  We  know,  too,  that  when  first  exposed  to  a  cold 
temperature,  the  surface  of  the  body  becomes  pallid.  These 
changes  in  color  are  due  to  the  action  of  the  muscles  in  the 
walls  of  the  arteries.  Heat  causes  the  muscles  to  relax, 
.thus  allowing  a  greater  quantity  of  blood  to  flow  through 
the  tissue;  cold,  on  the  other  hand,  stimulates  the  arteries 
to  contraction.  If,  however,  the  cold  temperature  is  not  too 
great,  the  walls  of  the  arteries  soon  relax,  and  one  feels  a 
warm  glow  all  over  the  body.  These  facts  will  be  referred 
to  again  in  the  discussion  of  bathing  (p.  240). 


152  STUDIES   IN  PHYSIOLOGY 

Colds  and  their  Prevention.  —  Prolonged  exposure  to  cold, 
the  wearing  of  wet  clothing,  or  sudden  exposure  to  a  draught 
of  air  often  results  in  a  contraction  of  the  arteries  in  the 
skin.  The  blood  is  thus  driven  away  from  the  surface  to 
the  internal  organs  of  the  body,  and  a  condition  of  conges- 
tion in  these  organs  is  the  result.  We  describe  this  condition 
as  a  "  cold."  The  real  cause  of  colds  is  not  yet  fully  under- 
stood. It  is  probable,  however,  that  frequently  the  conges- 
tion of  the  internal  organs,  which  may  follow  an  exposure, 
favors  the  growth  of  disease  producing  bacteria,  should  these 
be  present  in  the  air  passages  or  in  the  alimentary  canal. 

Those  who  are  accustomed  to  taking  vigorous  exercise 
followed  by  cold  baths  are  less  liable  to  colds.  The  wearing 
of  woolen  underclothing  is  another  means  of  prevention, 
since  this  material,  unlike  cotton  and  linen,  does  not  allow 
the  skin  to  be  acted  upon  quickly  by  sudden  changes  of 
temperature.  It  is 'without  doubt  unwise  to  keep  the  neck 
and  throat  muffled  with  furs  or  other  wrappings ;  for  when 
they  are  removed  the  sensitive  skin  is  more  easily  affected 
by  a  slight  draught. 

Effect  of  Exercise  on  the  Heart.1  —  The  pulse  rate  is  slowest 
when  we  are  asleep.  As  the  activities  of  the  day  begin, 
the  heart  beat  is  quickened,  and  after  violent  exercise  this 
organ  may  beat  as  often  as  twice  to  three  times  a  second. 
Exercise,  when  properly  regulated,  is  undoubtedly  bene- 
ficial to  every  organ  in  the  body;  for  a  higher  pulse  rate 
means  that  the  blood  is  renewed  in  each  tissue  so  much  the 
oftener,  that  more  oxygen  is  received  from  the  lungs,  and 
that  more  waste  matters  are  excreted.  Heart  muscle  itself, 
as  well  as  other  organs,  profits  by  this  increased  activity. 

Effect  of  Exercise  on  the  Size  of  the  Blood  Vessels.  —  When 
one  is  using  one's  muscles,  greater  metabolism  of  the  tissues 
goes  on,  and  a  larger  amount  of  blood  is  needed  to  supply 
material  for  repairing  the  waste.  The  sympathetic  nervous 
system  therefore  causes  the  muscular  walls  of  the  arteries  to 
1  See  "  Laboratory  Exercises,"  No.  29. 


A  STUDY  OF  THE  CIRCULATION  OF  BLOOD   153 

relax  in  the  organs  that  are  active.  It  is  manifestly  impos- 
sible to  have  an  increased  supply  of  blood  in  the  organs  of 
digestion  in  the  muscles,  and  in  the  brain  all  at  the  same 
time.  This  is  the  reason  why  it  is  unhygienic  for  an  adult 
to  exercise  violently  or  to  carry  on  any  considerable  degree 
of  mental  activity  immediately  after  eating.  Persistence  in 
violating  this  rule  usually  results  in  attacks  of  indigestion. 

An  important  advantage  of  proper  methods  of  exercise 
comes  from  the  fact  that  the  blood  is  thus  pushed  onward 
through  the  veins  and  the  lymph  through  the  lymphatics. 
Most  of  the  effect  of  the  pulse  beat  is  lost  before  the  blood 
reaches  the  capillaries,  and  much  of  the  force  exerted  on  the 
veins  and  the  lymphatics  comes  from  the  pressure  of  the 
overlying  muscles.  The  valves  in  these  tubes  prevent  a  back- 
ward flow.  Hence  the  blood  and  lymph  are  constantly 
pushed  on  toward  the  heart  by  the  muscular  pressure  upon 
the  veins  and  lymphatics,  a  pressure  which  is  increased  by 
exercise. 

Treatment  of  Cuts  and  Bruises.  —  One  can  tell  when  an  artery 
has  been  cut  by  the  fact  that  blood  comes  out  in  spurts. 
Since  the  blood  is  on  its  way  from  the  heart,  the  flow  can  be 
stopped  or  lessened  in  this  kind  of  accident  by  applying 
pressure  on  the  side  of  the  wound  nearest  the  heart.  Thus 
if  the  finger  is  cut  deeply  and  the  blood  jets  forth,  a  strong 
cord  or  a  handkerchief  should  be  tied  loosely  about  the  wrist, 
and  a  pencil  or  piece  of  wood  should  be  placed  beneath,  and 
then  the  bandage  should  be  twisted  until  the  blood  flow  is 
stopped  by  the  pressure.  When  blood  flows  evenly  from  a 
wound,  it  is  an  indication  that  a  vein  has  been  cut,  and  the 
pressure  should  be  applied  in  a  similar  way  on  the  side  away 
from  the  heart. 

Bleeding  from  the  nose  can  usually  be  stopped  by  hold- 
ing the  head  erect,  and  by  applying  cold  water  to  the  bridge 
of  the  nose  or  to  the  back  of  the  neck. 

In  case  of  a  cut  or  of  a  bruise  in  which  the  skin  is  broken, 
the  wound  should  be  cleansed  as  quickly  as  possible  with 


154  STUDIES  IN  PHYSIOLOGY 

corrosive  sublimate,  carbolic  acid,  or  some  other  germ-de- 
stroying solution.  Antiseptic  tablets  can  be  obtained  at  any 
drug  store,  and  a  solution  can  be  made  by  dissolving  a  tablet 
in  a  pint  of  water.  This  should  be  kept  on  hand  and  used 
to  wash  out  wounds.  The  injury  should  then  be  covered 
with  cotton  soaked  in  the  poison  solution  and  bandaged,  to 
prevent  the  entrance  of  other  germs.  If  this  is  not  done, 
bacteria  are  likely  to  settle  in  the  wound,  and  healing  may 
be  delayed  or  even  more  serious  results  may  follow.  With 
proper  treatment  a  wound  should  show  no  signs  of  the 
formation  of  pus,  should  not  cause  pain,  and  should  heal 
rapidly. 

Effect  of  Alcohol  on  the  Organs  of  Circulation.  — Alcohol  "  ex- 
cites the  vascular  system,  accelerates  the  circulation,  so  that 
the  muscles  and  nerves  are  more  active,  owing  to  the  greater 
supply  of  blood.  It  also  gives  rise  to  a  subjective  feeling  of 
warmth.  In  large  doses,  however,  it  paralyzes  the  vessels, 
so  that  they  dilate,  and  thus  much  heat  is  given  off  and  the 
temperature  is  lowered.1  The  action  of  the  heart  also  be- 
comes affected,  the  pulse  becomes  smaller,  feebler,  and  more 
rapid."  —  "  Text-book  of  Human  Physiology,"  LANDOIS  and 
STERLING. 

6.  A  COMPARATIVE  STUDY  OF  THE  CIRCULATION 

Circulation  in  the  Earthworm.  —  If  we  examine  the  upper 
or  dorsal  surface  of  a  living  earthworm,  we  see  through  the 
skin  a  tube  through  which  the  blood  is  driven  in  pulses. 
This  is  called  the  dorsal  blood  vessel.  Near  the  anterior  end 
of  the  body,  five  pairs  of  large  blood  vessels  (a-or'tic  arches) 
branch  off  from  the  dorsal  blood  vessel  just  mentioned,  sur- 
round the  esophagus,  and  connect  with  a  large  blood  tube 
that  lies  beneath  the  alimentary  canal.  The  aortic  arches 
pulsate  like  the  dorsal  blood  vessel,  and  thus  help  to  force 
the  blood  through  the  body.  Branches  of  the  dorsal  and 

i  For  discussion  of  effect  of  alcohol  on  body  temperature,  see  p.  243. 


A  STUDY  OF  THE  CIRCULATION  OF  BLOOD   155 


m — 


ventral  blood  vessels  carry  blood  to  the  capillaries  in  all 
parts  of  the  body.  The  earthworm, 
then,  has  no  heart,  and  it  is  there- 
fore impossible  to  distinguish  arteries 
from  veins.  The  blood  is  propelled 
through  the  body  by  the  rhythmical 
contraction  of  the  muscular  walls  of 
the  dorsal  blood  vessel  and  of  the 
five  aortic  arches  described  above.  It 
has  been  proved  that  the  blood  flows 
through  the  dorsal  vessel  from  the  tail 
toward  the  head  end  of  the  worm, 
whence  it  is  driven  down  to  the  ventral 
vessel  by  the  contraction  of  the  aortic 
arches.  The  course  of  the  blood  back 
to  the  dorsal  tube  is  still  a  matter  of 
dispute. 

Circulation  in  the  Fish. — The  structure 
of  the  fish  heart  is  relatively  simple. 
It  lies  near  the  ventral  surface  and  has 
a  single  auricle  and  a  single  ventricle. 
When  the  ventricle  contracts,  the 
blood  is  forced  forward  a  short  distance 
through  an  artery,  which  soon  divides 
into  a  series  of  branches  on  each  side  of 
the  body.  By  these  arteries  the  blood 
passes  in  a  dorsal  direction  through  the 
gills,  where  it  loses  some  wastes  and 
receives  the  oxygen  that  is  dissolved  in 
the  water.  The  gill  arteries  finally 
empty  into  the  dorsal  aorta,  from  which 
blood  is  distributed  to  all  parts  of  the 
body.  From  the  systemic  capillaries 
it  is  brought  back  to  the  auricle  by 
veins  of  very  large  size.  Hence  the  two  systems  of  circula- 
tion (called  in  man  the  pulmonary  and  systemic),  instead  of 


FIG.    60.  —  Circulation 
in  the  Fish. 

a,  b  =  arteries  to  gills. 

c  =  ventricle. 

d—  auricle. 

e  =  opening  of  veins 
into  auricle. 

/=  portal  veins. 

g  =  intestine. 

h  =  vena  cava. 

k  =  abdominal  aorta. 

I  =  kidneys. 
m  =  aorta  which  sup- 
plies region  of 
tail. 


156 


STUDIES   IN  PHYSIOLOGY 


being  carried  on  side  by  side  as  in  the  higher  vertebrates, 
are  arranged,  so  to  speak,  one  behind  the  other,  or  tandem, 
and  the  blood  is  driven  successively  through  the  gill  and 
systemic  capillaries  by  the  contraction  of  a  single  ventricle. 
Circulation  in  the  Frog.  —  In  the  frog's  heart  there  are  three 
chambers,  namely,  two  auricles,  and  a  single  ventricle.  The 


Art 


rtery  tos/ght  lung  -  .  X/    * 
ar?as/</ri  ~---; 


ft/gfrt  auric/e 

Artery  ton'§ht  or/n>^ 

flight  lung 


Artery  to  left 
'Jung  and stin 


Artery  tp  left  arm 
teftaur/c/e 
'  Mentric/e 


— -/.efttvny 
--Dorsa/aorto 


--.~Arterits  to 

A/d/ieys 


Mcf/ieys 


FIG.  61.  —  Arteries  in  the  Circulation  of  the  Frog. 

left  auricle,  as  is  the  case  in  the  human  heart,  receives  the 
blood  that  has  taken  up  oxygen  in  the  lungs,  while  to 
the  right  auricle  comes  the  blood  from  the  other  organs  of 
the  body.  Both  these  auricles  send  the  blood  they  receive 
into  the  single  ventricle,  and  so  the  oxygenated  blood  is 
mixed  more  or  less  with  blood  that  has  been  deprived  of 
oxygen  during  its  course  through  the  body.  By  a  compli- 
cated system  of  valves,  however,  the  blood  that  has  the 


A  STUDY  OF  THE    CIRCULATION  OF   BLOOD       157 

most  oxygen  is  switched  off  into  the  arteries  that  go  to 
the  head;  the  blood  supplied  with  a  moderate  amount  of 
oxygen  is  forced  to  the  stomach,  intestines,  and  other  organs 
in  the  lower  part  of  the  body;  while  the  blood  with  the 
least  oxygen  is  turned  into  the  arteries  that  carry  it  to  the 
lungs.  Blood  from  the  lungs  then  returns,  as  stated  above, 
through  pulmonary  veins  to  the  left  auricle ;  the  rest  of  the 
blood  conies  back  to  the  right  auricle. 

Circulation  in  the  Reptiles. — In  the  group  of  reptiles  (snakes, 
alligators,  turtles)  we  first  find  the  beginnings  of  a  four- 
chambered  heart.  But  while  the  two  auricles  are  entirely 
separated  from  each  other,  the  partition  between  the  ven- 
tricles is  not  quite  complete.  In  spite  of  this  fact,  the  pul- 
monary and  systemic  circulations  are  carried  on  without 
any  considerable  mixing  of  blood  in  the  two  sides  of  the 
ventricle.  As  in  man,  the  right  side  of  the  heart  has  to  do 
with  sending  the  blood  to  the  lungs  for  oxygen;  the  left 
side  supplies  the  rest  of  the  body  with  the  oxygenated  blood. 

Circulation  in  the  Birds  and  Mammals.  —  All  birds  and  all 
mammals  (including  man)  have  the  two  sides  of  the  heart 
completely  separated  from  each  other.  There  are,  there- 
fore, two  distinct  auricles,  each  communicating  with  one 
ventricle  only.  Hence,  we  may  speak  of  a  distinct  right 
and  left  heart  in  all  animals  above  the  group  of  reptiles. 

Comparison  of  the  Organs  of  Circulation  Studied. — Reviewing 
the  facts  presented  above,  we  see  that,  while  in  each  of  the 
animals  studied  there  is  a  complete  circulation  of  the  blood, 
the  means  by  which  this  circulation  is  accomplished  varies 
greatly.  In  the  earthworm  the  force  that  propels  the  blood 
is  furnished,  not  by  a  heart,  but  by  the  contraction  of  the 
muscular  walls  of  certain  blood  vessels. 

All  vertebrates  (fishes,  amphibia,  reptiles,  birds,  and  mam- 
mals) have  hearts,  and  this  is  also  true  of  many  kinds  of  in- 
vertebrates. But  one  has  only  to  compare  the  different 
hearts  we  have  described  to  see  how  much  this  organ  may 
be  modified  in  structure.  Fishes  have  a  single  auricle  and 


158  STUDIES   IN  PHYSIOLOGY 

a  single  ventricle.  In  frogs  and  toads  (the  amphibia)  we 
find  the  beginnings  of  a  right  and  left  heart.  But  while 
the  separation  of  the  auricles  is  complete,  the  two  kinds  of 
blood  are  mixed  in  the  single  ventricle.  The  two  sides  of 
the  heart  are  more  completely  separated  in  the  reptiles,  and 
when  we  come  to  the  birds  and  mammals  we  find  that  there 
is  no  means  of  direct  communication  between  the  right  and 
left  hearts.  Hence,  in  the  highest  groups,  there  is  a  dis- 
tinct pulmonary  and  systemic  circulation. 

In  our  comparative  study  of  digestion,  we  noted  an  increas- 
ing complexity  of  structure  from  the  earthworm,  through 
the  frog  and  bird,  to  the  mammal.  The  same  fact  is  evi- 
dent in  considering  the  various  circulatory  systems.  The 
higher  animals  have  more  complete  machinery  for  doing 
the  work  of  the  body,  and  for  this  reason  they  can  carry  on 
the  processes  of  life  more  perfectly. 


CHAPTER   IX 


A  STUDY  OF  THE  SKELETON 

X-Ray  Pictures.  —  One  of  the  marvelous  discoveries  of  the 
closing  years  of 
the  last  century 
was  that  of  the 
so-called  X-rays. 
If,  when  a  sen- 
sitive photo- 
graphic plate  is 
held  in  position 
behind  a  man, 
these  electrical 
rays  are  focused 
upon  any  part  of 
his  body  the 
hand  for  in- 
stance, a  picture 
is  produced  on 
the  plate  like 
that  shown  in 
Fig.  62.  One  can 
see  the  faint  out- 
lines of  the  hand, 
and  within  it  a  clear  picture  of  the  bony  skeleton  that  forms 
its  framework. 

The  Uses  of  the  Bony  Framework  of  the  Body.  —  In  certain 
regions  of  the  body,  bones  surround  and  protect  delicate 
organs.  The  brain,  for  example,  is  inclosed  within  a  bony 
box ;  the  eyes  are  set  into  deep  sockets ;  the  delicate  mech- 

159 


FIG.  62.  — X-Ray  Picture  of  the  Hand. 


160  STUDIES   IN  PHYSIOLOGY 

anism  of  the  inner  ear  is  hidden  within  the  hardest  bone  of 
the  body ;  and  the  organs  of  the  chest  cavity  are  well  pro- 
tected by  the  ribs  and  breastbone. 

In  other  parts  of  the  body,  as  in  the  arms  and  legs,  the 
skeleton  is  surrounded  by  the  muscles,  nerves,  and  other 
tissues.  Here  the  bones  act  as  levers,  which  are  moved  by 
the  muscles  whenever  we  wish  to  go  from  place  to  place,  or 
whenever  we  desire  to  move  things  about  us. 

In  a  word,  then,  the  bony  framework  (1)  gives  to  the  body 
its  permanent  shape,  (2)  protects  delicate  organs,  (3)  pro- 
vides a  leverage  on  which  muscles  may  act. 

Regions  of  the  Skeleton.  —  For  convenience,  the  two  hun- 
dred bones  of  the  skeleton  may  be  divided  into  three  groups, 
namely,  (1)  the  bones  of  the  arms  and  legs,  (2)  the  bones  of 
the  neck  and  trunk,  and  (3)  the  bones  of  the  head  (Fig.  63). 

1.    THE  SKELETON  OF  THE  AKMS  AND  LEGS 

Bones  of  the  Arm.  —  The  skeleton  of  the  upper  arm  (see 
Fig.  64,  B)  is  formed  by  a  single  long  bone  called  the  hu'me- 
ruSj  which  extends  from  the  shoulder  to  the  elbow.  In  the 
forearm,  one  can  feel  through  the  flesh  two  separate  long 
bones,  of  about  the  same  size,  lying  side  by  side ;  the  bone 
on  the  thumb  side  of  the  forearm  is  the  ra'di-us  ;  on  the  little 
finger  side  is  the  ul'na.  Two  rows  of  small  bones,  more  or 
less  cubical  in  shape,  are  found  in  the  wrist.  These  eight 
wrist  or  car'pal  bones  move  freely  upon  each  other,  and  thus 
give  the  hand  a  great  range  of  movement.  By  pressing  with 
the  finger  on  the  back  of  the  hand,  one  can  distinguish  five 
rather  long  bones,  and  since  these  lie  beyond  or  distal  to 
the  carpals  they  are  called  met-a-car'pal  bones  (Greek  meta= 
beyond  +  karpds  =  wrist).  The  skeleton  of  each  finger  is 
formed  of  three  separate  bones,  and  in  the  thumb  there  are 
two  bones.  These  fourteen  bones  of  the  digits  are  called 
pha-lan'ges  (because  of  the  arrangement  of  bones  in  succes- 
sive rows  like  the  soldiers  in  the  Greek  phalanx). 


A  STUDY   OF  THE   SKELETON 


161 


NASAL 


SHOULDER    BLADE  - 
(SCAPULA) 


•--SUPERIOR  MAXILLARY  BONES 

^"^--iNFERlOR  MAXILLARY  BONE 

SPINAL  COLUMN. CERVICAL  REGION. 
^-(CLAVICLE)  COLLAR  BONE 


FIG.  63.  —  Bones  of  the  Skeleton. 


162  STUDIES  IN  PHYSIOLOGY 

Bones  of  the  Leg.  —  In  the  upper  part  of  the  leg  (see  Fig. 
64,  A)  is  a  single  bone,  the  thigh  bone  or  fe'mur.  This  cor- 
responds  in  position  to  the  humerus  of  the  arm,  but  it  is 
longer  and  stouter  than  the  latter ;  in  fact,  it  is  the  longest 
bone  in  the  body.  The  skeleton  in  the  calf  of  the  leg  con- 
sists of  two  bones,  tib'i-a  and  fib'u-la,  which  have  a  position 
similar  to  that  of  the  radius  and  ulna.  The  tibia  is  on  the 
inner  or  great-toe  side  and  is  much  larger  than  the  slender 
fibula.  At  the  kneejoint  one  can  feel  a  flat  piece  of  bone, 
more  or  less  circular  in  outline,  called  the  kneecap  or  pa-tel'la. 
When  one  extends  the  knee  and  rests  the  heel  on  the  floor, 
the  kneecap  can  be  easily  moved  about  over  the  kneejoint. 
There  are  seven  tar 'sal  bones  in  the  ankle,  which  like  the 
carpals  have  a  somewhat  cubical  form.  They  are,  however, 
larger  and  less  movable  than  the  eight  carpal  bones  of  the 
wrist.  One  end  of  the  arch  of  the  foot  rests  upon  the  heel 
bone,  the  largest  of  the  ankle  bones.  The  arch  is  completed 
by  the  other  tarsal  bones,  and  by  five  rather  slender  met-a- 
tar'sals  (Greek  meta  =  beyond  -f  tarsds  =  ankle).  The  great 
toe  has  two,  and  each  of  the  other  toes  three  phalanges, 
making  the  same  number  of  bones  in  the  fingers  and  toes. 

2.   THE  SKELETON  OF  THE  NECK  AND  TRUNK 

The  Spinal  Column. — The  erect  position  of  the  adult  human 
body  is  maintained  by  a  column  of  bones  called  vertebrae 
(Latin  vertere  =  to  turn,  so  called  because  these  bones  may 
be  turned  more  or  less  on  each  other).  The  spinal  column 
can  be  felt  through  the  skin  behind  the  neck  and  down  the 
middle  of  the  back. 

In  the  neck  region  are  seven  bones  called  cer'vi-cal  verte- 
brae (Latin  cervix  =  neck) ;  twelve  dor' sal  vertebrae  carry  the 
twelve  pairs  of  ribs ;  and  in  the  loins  are  the  five  large  lum'- 
bar  vertebrae  (Latin  lumbus  =  loin) .  Below  the  lumbar 
bones  is  a  single  bone  called  the  sa'crum.  When  one  exam- 
ines it,  however,  four  ridges  and  four  pairs  of  holes  are 


A   STUDY   OF   THE   SKELETON 


163 


inn 


car  =  carpal    or    wrist 
bones. 

cl  =  clavicle  or  collar 
bone. 

fern  =  femur    or    thigh 
bone. 

Jib  =  fibula. 

hum  =  humerus     (upper 
arm  bone) . 

inn  =  pelvic  bone. 

metac  =  metacarpal        or 
palm  bones. 

metat  =  metatarsal  bones 
(sole  of  foot) . 

pat  =  patella    or    knee 
cap. 

phi  =  phalanges  of  fin- 
gers and  toes. 

rad  —  radius. 

scap  =  scapula  or  shoul- 
der blade. 

tib  =  tibia. 
uln  =  ulna. 


FIG.  64.  — Bones  of  Left  Arm  (B)  and  of  Leg  (A)  together  with  Bones  of 

Girdles. 


evident,  which  indicate  the  regions  where  the  five  sepa- 
rate vertebrae  that  are  found  in  the  sacrum  of  a  child  have 
grown  together.  Posterior  to.  the  sacrum  in  a  child's  skele<- 


164 


STUDIES  IN  PHYSIOLOGY 


11. 


12 


C...J 


FIG.  65.  —Spinal  Column. 

A  =  side  view,  showing  curves.  S  =  sacrum. 

B  =  dorsal  view,  showing  width  of  vertebrae.    (7  =  coccyx. 
C.  1-7  =  7  cervical  vertebrae.  sp  =  spinous  process. 

D.  1-12  =  12  dorsal  vertebrae.  tr  =  transverse  process. 

L.  1-5  =  5  lumbar  vertebrae. 


A  STUDY   OF   THE    SKELETON 


165 


tr 


ton  are  four  bones,  which  in  the  adult  become  united  in 
one.  From  a  fancied  resemblance  to  a  cuckoo's  bill,  this 
part  of  the  spinal  column  is  called  the  coc'cyx  (from  Greek, 
meaning  cuckoo).  Hence,  in  the  spinal  column  of  a  child 
there  are  thirty-three  separate  bones;  in  that  of  an  adult, 
twenty-six  including  sacrum  and  coccyx. 

The  Structure  of  a  Vertebra. — The  vertebrae  are  among 
the  most  irregular  bones  of  the  body.  In  general  one  may 
say  that  each  consists  of  two  parts ;  namely,  a  mass  of  bone 
called  the  cen'trum  or  body,  and  a  bony  arch  with  seven  irregu- 
lar processes.  To 
this  region  of  the 
vertebra  is  given 
the  name  neu'ral 
arch)  because  it 
helps  to  inclose 
the  neural  or  spinal 
cord.  The  centrum 
is  on  the  ventral 
side  of  the  spinal 
column ;  circular 
in  outline,  it  is  flat- 
tened above  and 
below,  and  on  these  surfaces  are  pads  of  cartilage  that  allow 
the  vertebrae,  to  a  certain  extent,  to  turn  and  bend  on  each 
other.  The  weight  of  the  body  is  supported  by  the  body 
of  the  vertebra. 

From  the  neural  arch,  as  already  stated,  project  seven 
processes.  One  of  these  is  the  spi'nous  process,  which  can 
be  felt  in  the  middle  of  the  back.  It  is  this  succession  of 
processes  that  has  suggested  the  name  spinal  column.  Two 
lateral  processes  extend  from  the  side  of  the  neural  arch,  and 
to  these  processes  the  ribs  are  attached  in  the  dorsal  region 
of  the  spinal  column.  The  other  four  projections  from  the 
arch  of  the  vertebra  are  called  ar-tic'u-lar  processes  ;  two  of 
them  face  dorsally,  the  other  two  ventrally.  Since  they 


FIG.  66. —  Parts  of  a  Vertebra. 

A  =  side  view.  ar  =  articular  process. 

B  =  top  view.  6  =  body  or  centrum. 

n  =  neural  ring  (containing  spinal  cord) . 
sp  =  spinous  process.         tr  —  transverse  process. 


166 


STUDIES  IN  PHYSIOLOGY 


meet  corresponding  processes  on  other  vertebrse,  they  allow 
these  bones  to  move  or  articulate  upon  each  other. 

The  Structure  of  Atlas  and  Axis.  —  The  two  top  vertebrse 
have  a  peculiarly  modified  structure,  which  allows  the  nod- 
ding and  turning  movements  of  the  head.  The  skull  rests 
upon  the  first  cervical  vertebra ;  it  is  called  the  atlas  (Fig. 

67,  a).  This  name  was  sug- 
gested by  one  of  the  myths 
of  ancient  history,  in  which 
the  hero  Atlas  is  said  to 
have  supported  the  world 
on  his  shoulders.  When  we 
nod,  in  saying  "yes,"  the 
skull  rocks  backward  and 
forward  on  the  atlas.  In 
signifying  "no,"  on  the 
other  hand,  the  atlas  turns 
about  a  projecting  peg  (Fig. 
67,  c)  on  the  top  of  the 
second  vertebra  (Fig.  67,  &).  Hence,  the  second  cervical 
vertebra  is  called  the  axis.  When  the  head  is  tilted  from 
side  to  side,  the  motion  involves  several  of  the  cervical 
vertebrse. 

Adaptations  shown  in  the  Spinal  Column.  —  The  human 
spinal  column  is  a  wonderful  piece  of  mechanism,  which  by 
its  structure  is  adapted  to  perform  at  the  same  time  three 
distinct  functions.  In  the  first  place,  we  have  seen  that  the 
bodies  of  the  vertebrce,  piled  one  on  the  other,  form  a  column 
strong  enough  to  support  the  weight  of  the  body.  In  the  neck 
region  the  vertebrse  are  relatively  small  (Fig.  65) ;  but 
through  the  dorsal  region  their  size  increases,  until  in  the 
last  lumbar  vertebra  we  find  the  largest  centrum  in  the  series. 
The  spinal  column,  therefore,  forms  a  cone  with  the  base 
made  by  the  five  sacral  bones  united  into  one ;  to  this  solid 
base  the  legs  are  attached. 

Again,  the  structure  of  the  spinal  column  shows  marvel- 


FIG.  67.  —  Atlas  and  Axis  Vertebrse. 

«  =  atlas,  on  which  rests  the  skull. 
b  =  axis,  about  which  atlas  turns, 
c  =  peg  of  axis  projecting  upward 
through  hole  in  atlas. 


A   STUDY  OF  THE   SKELETON 


167 


ous  provisions  for  securing  elasticity  and  freedom  of  motion. 
Elasticity  is  secured  by  a  succession  of  four  curves  which 
are  best  seen  in  a  side  view  of  the  body  (Fig.  65,  A).  By 
means  of  these  curves  the  head  and  the  upper  part  of  the 
trunk  are  saved  from 
sudden  shocks  that  would 
result  from  running  or 
jumping,  for  the  curves 
act  like  a  series  of 
springs.  The  cartilage 
pads,  likewise,  serve  as 
cushions  to  prevent  jar- 
ring. That  a  consider- 
able range  of  movement 
is  allowed  by  the  struc- 
ture of  the  vertebral  col- 
umn will  be  evident  after 
a  trial  by  each  student. 
With  the  heels  together, 
and  the  hips  held  firm, 
one  can  bend  the  body 
forward  and  backward, 
and  from  side  to  side; 
and  the  whole  pile  of 
bones  can  also  be  twisted 
around  sufficiently  to  al- 
low one  to  look  behind 


FIG.  68.  —Spinal  Column,  Ribs,  and  Ster- 
num. 

a-b  =  spinal  column. 

c=  breastbone  (sternum). 
d  =  cartilage  of  true  rib. 
e  =  united  cartilages  of  false  ribs. 
1-7  =  true  ribs  with  distinct  cartilages. 
8-10  =  false  ribs,  cartilages  united. 
11-12  =  floating  ribs. 


oneself. 

A  third  adaptation  that 
is  evident  in  the  structure 
of  the  spinal  column  is  the  protection  it  affords  for  the  delicate 
spinal  cord.  The  series  of  neural  arches  and  vertebral  bodies 
form  a  more  or  less  continuous  tube,  within  which  lies  the 
spinal  cord.  Connected  with  this  part  of  our  nervous  system 
are  thirty-one  pairs  of  spinal  nerves,  which  pass  out  from 
the  sides  of  the  tube  in  which  the  cord  lies  by  holes  between 


168 


STUDIES   IN  PHYSIOLOGY 


each  two  vertebrae.  For  this  reason  the  perforations  are 
called  in-ter-ver'te-bral  fo-ram'i-na  (Latin  inter  =  between  -|- 
vertebrce  =  vertebrae  -{-foramina  =  holes). 

One  would  search  far  before  finding  a  more  perfect  means 
of  securing  strength,  elasticity,  and  flexibility  than  that  pro- 
vided in  the  structure  of  the  human  spinal  column. 

The  Ribs  and  Sternum . —  Attached  to  the  transverse  pro- 
cesses of  each  of  the  twelve  dorsal  vertebrae,  is  a  pair  of 

slender,  curved 
bones  called  the 
ribs.  The  first 
seven  pairs  bend 
around  the  sides 
of  the  chest  cav- 
ity and  are  at- 
tached by  means 
of  cartilage  to  the 
dagger-shaped 
breastbone  or 
ster'num.  The 
cartilages  of  the 
eighth,  ninth, 
and  tenth  pairs 
are  joined  on 
each  side  into 
one,  and  this  is 
attached  to  the 
cartilage  of  the 
seventh  pair. 
The  eleventh  and 
twelfth  pairs  are 
called  floating  ribs  because  they  have  no  connection  with  the 
breastbone  (see  Fig.  68).  The  ends  of  these  ribs  can  easily 
be  felt  through  the  body  wall  on  either  side  of  the  trunk. 

The  Pectoral  Girdle.  —  We  began  our  study  of  the  skeleton 
by  a  consideration  of  the  bones  of  the  arm.  We  are  now  to 


FIG.  69.  —  Attachment  of  Ribs. 

6  =  body  of  dorsal  vertebra. 

c  =  cartilage  connecting  rib  to  breastbone 

r=rib. 

st  =  sternum  or  breastbone. 

tr  =  transverse  process  of  vertebra. 


A   STUDY   OF   THE   SKELETON  169 

see  how  the  arm  is  attached  to  the  rest  of  the  skeleton.  Ly- 
ing outside  the  ribs  at  the  anterior  end  of  the  trunk  are  two 
flat,  triangular  shoulder  blades  (each  called  a  scap'u-la)  (Fig.  64, 
scap)  and  two  slender  collar  bones  (each  called  a  clavicle) 
(Fig.  64,  cf).  The  /-shaped  collar  bones  are  attached  ven- 
trally  to  the  breastbone,  while  the  other  end  of  each  is 
joined  to  one  of  the  shoulder  blades.  In  this  way  an  incom- 


5LV  ,M  disc 


is 
FIG.  70.  — Bones  of  the  Pelvic  Girdle  (Ventral  View). 

acet  =  socket  of  pelvic  bone  into  which  fits  head  of  femur, 
cocc  =  coccyx.  disc  —  cartilage  disk  between  vertebrae. 

il,  is,  pu  =  parts  of  pelvic  bone.       sac  =  sacrum. 
5LV=  fifth  lumbar  vertebra. 

plete  circle  of  bones  is  formed  to  which  is  given  the  name 
pec'to-ral  girdle  (Latin  pectoralis,  referring  to  the  chest).  A 
shallow  socket  is  found  on  the  outside  of  each  shoulder 
blade,  and  into  this  fits  the  proximal  end  of  a  humerus 
bone.  It  will  be  seen  that  the  pectoral  girdle  is  directly 
attached  to  the  rest  of  the  skeleton  only  by  the  ventral 
ends  of  the  collar  bones.  Great  freedom  of  motion  for  the 
arms  is  therefore  possible,  since  the  girdle  itself  is  movable. 


170  STUDIES  IN  PHYSIOLOGY 

The  Pelvic  Girdle.  —  A  complete  girdle  of  bones  is  formed 
at  the  posterior  end  of  the  trunk  by  the  two  pelvic  bones 
which  are  attached  dorsally  to  the  sacrum  and  which  meet 
in  front.  The  upper  edge  of  these  bones  can  be  felt  at  the 
hips  (Fig.  TO,  'if).  On  the  outer  side  of  each  pelvic  bone  is 
a  deep  socket  (Fig.  70,  acet)  into  which  fits  the  proximal  end 
of  the  femur.  Since  the  pelvic  girdle  is  not  movable  like 
the  pectoral,  the  body  has  a  firm  base  Of  support.  The 
range  of  movement  of  the  leg,  however,  is  relatively  small 
in  comparison  with  that  of  the  arm. 

3.   THE  SKELETON  OP  THE  HEAD 

Two  groups  of  bones  may  be  distinguished  in  the  skull  or 
skeleton  of  the  head,  namely,  the  bones  forming  the  cranium 
which  surrounds  and  protects  the  brain,  and  the  bones  that 
form  the  skeleton  of  the  face. 

The  Bones  of  the  Cranium.  —  The  cranium  is  a  more  or  less 
spherical  box,  composed  of  eight  bones  as  follows:  The 
fron'tal  (Latin  frons,  frontis  =  forehead)  forms  the  forehead 
and  the  top  of  the  eye  sockets.  A  pair  of  pa-ri'e-tal  bones 
(Latin  paries,  parietis  =  a  wall)  make  up  the  principal  part  of 
the  side  walls  of  the  cranium  and  meet  along  the  top  of  the 
skull.  On  each  side  below  the  parietals,  lies  one  of  the  tem'- 
po-ral  bones.  The  temporal  bones  contain  the  cavities  in 
which  lie  the  most  delicate  parts  of  the  ear.  The  oc-cip'i-tal 
(Latin  ob  =  against  +  caput  =  head)  forms  the  posterior  part 
of  the  dorsal  region  of  the  brain  box.  In  this  bone  is 
a  large  opening,  the  fo-ra'men  magnum  (Latin  magnum  = 
great  +  foramen  —  hole),  through  which  the  spinal  cord 
passes  to  connect  with  the  brain.  The  sphe'noid  is  a  very 
irregular  bone  shaped  more  or  less  like  a  butterfly;  this 
with  the  eth'moid  makes  a  floor  for  the  cranium,  and  in 
front  toward  the  ventral  surface  separates  the  brain  from 
the  nose  cavity.  The  brain  is  therefore  inclosed  by  two 
pairs  of  bones  (the  parietals  and  temporals)  and  by  four 


A   STUDY   OF  THE   SKELETON 


173 


single  bones  (the  frontal,  occipital,  sphenoid,  and  ethmoid). 
In  addition  to  these  eight,  there  are  within  the  temporal 
bones  three  very  small  bones  in  the  middle  region  of  each 
ear  cavity  (see  p.  309). 

The  Bones  of  the  Face.  —  Twelve  of  the  fourteen  face  bones 
are  in  pairs.  The  two  cheek  bones  or  malar  bones  lie  on  the 
outer  and  lower  sides  of  the  eye  sockets.  The  bridge  of  the 


FIG.  71.  —  Bones  of  Skull. 

nose  is  made  by  the  pair  of  na'sal  bones.  Between  the  two 
halves  of  the  nose  is  a  single  thin  partition  of  bone  (the 
vo'mer),  and  on  the  outer  walls  of  each  nostril  chamber  are 
the  tur'bi-nate  or  spongy  bones  (see  Fig.  133).  A  small,  thin 
tear  bone  on  each  side  helps  to  form  the  separation  between 
the  eye  socket  and  the  nose,  while  the  two  paVate  bones 
lie  horizontally  between  the  nose  and  mouth  cavities.  And, 
finally,  there  are  two  halves  to  the  upper  jawbone  to  which 
are  united  the  upper  teeth,  and  a  single  lower  jawbone  or 
man'di-ble  in  which  the  lower  teeth  are  imbedded.  The 


172  STUDIES   IN  PHYSIOLOGY 

mandible  is  the  only  movable  bone  of  the  skull.  All  the 
others  are  united  by  irregular,  toothlike  processes  (called 
su'tures)  which  fit  closely  into  each  other,  like  the  dovetail 
joint  of  the  carpenter  (see  Fig.  71.) 

Adaptations  shown  in  the  Structure  of  the  Skull.  —  By  its 
rounded  contour,  the  skull  furnishes  the  best  possible  protec- 
tion for  the  brain.  In  the  first  place,  if  a  blow  strikes  upon 
the  head,  it  would  be  much  more  likely  to  glance  off  than 
would  be  the  case  if  the  sides  and  top  were  flat.  Again,  the 
arched  form  of  the  skull,  like  the  arch  of  a  bridge,  gives 
the  greatest  possible  strength  in  a  given  amount  of  material 
to  resist  the  force  of  a  hard  blow. 

Since  the  end  of  the  nose  and  the  outside  ear  are  the  most 
exposed  portions  of  the  head,  they  would,  if  made  of  bone,  be 
in  constant  danger  of  getting  broken.  Cartilage,  however, 
gives  them  sufficient  permanence  of  form,  and  at  the  same 
time  this  elastic  material,  if  bent  out  of  shape,  at  once 
returns  to  its  original  position  as  soon  as  the  pressure  is 
removed. 

The  deep  eye  sockets,  surrounded  by  frontal,  upper  jaw, 
and  cheek  bones,  seldom  allow  any  blow  to  injure  the  eye. 
The  drum  of  the  ear,  the  three  tiny  bones  of  the  middle  ear, 
and  the  delicate  mechanism  of  the  inner  ear  are  all  buried 
deep  in  the  lower  part  of  the  temporal  bone  which  is  the 
hardest  part  of  the  bony  skeleton,  and  so  these  are  out  of 
danger. 

4.   DIFFERENCES    BETWEEN    THE    SKELETON    OF   A    CHILD 
AND    THAT    OF    AN    ADULT 

Difference  in  Composition.  —  It  should  be  noted,  in  the  first 
place,  that  most  of  the  bones  of  the  skeleton  are  first  formed 
wholly  of  cartilage,  and  that  this  cartilage  is  gradually  re- 
placed by  bone  through  the  supply  of  mineral  matters  fur- 
nished by  the  blood.  This  explains  the  fact  that  the  bones 
of  young  children  are  easily  bent  without  being  broken,  while 
those  of  an  old  person  are  brittle  and  break  easily.  Because 


A   STUDY   OF  THE   SKELETON 


173 


cl 


of  this  fact,  young  children  should  not  be  urged  to  walk  at 
too  early  an  age,  lest  they  become  bow-legged. 

Differences  in  the  Skull.  —  In  the  top  of  a  very  young 
child's  head  is  a  space  between  the  frontal  and  parietal  bones, 
called  the  fon-ta-nelle'.  This  opening 
gradually  lessens  in  size  by  the  growth 
of  the  surrounding  bones  until  at  the 
end  of  the  first  or  second  year  it  is 
completely  closed. 

Differences  in  the  Spinal  Column. — 
We  have  already  noted  the  union  that 
takes  place  in  the  five  bones  of  the 
sacrum  and  in  the  four  bones  of  the 
coccyx.  These  consolidations  are  usu- 
ally completed  during  the  period  from 
the  eighteenth  to  the  thirtieth  year  of 
life. 

Differences  in  the  Breastbone.  —  In  dis- 
cussing the  breastbone,  we  compared 
with  its  shape  that  of  a  dagger.  This 
bone  also  in  childhood  is  formed  of 
several  distinct  parts.  The  four  pieces 
that  make  up  the  blade  of  the  dagger 
are  usually  united  by  the  twenty-fifth 
year,  but  a  succession  of  ridges  remain 
which  show  the  lines  of  union  (see 
Fig.  72).  The  handle  and  the  point 
of  the  dagger  often  remain  as  distinct 
pieces  until  old  age. 

Differences  in  the  Bones  of  Ann  and  of 
Leg.  —  At  the  proximal  end  of  the  ulna 
is  a  projection  of  bone  (commonly  known  as  the  "funny 
bone")  which  is  readily  felt  at  the  elbow.  Throughout 
early  life  this  bone  is  separate  from  the  ulna  and  hence 
it  corresponds  to  the  position  of  the  kneecap  in  the  leg. 
It  becomes  united  with  the  ulna  at  about  the  sixteenth 


FIG.    72.  —  Sternum 
viewed  from  Front. 

cl  =  places    of   attach- 
ment  of    collar 
bones  (clavicles). 
x  =  lower     projecting 

end. 

1-7  =  places  of  attach- 
ment of  first 
seven  ribs. 


174 


STUDIES  IN  PHYSIOLOGY 


In  the  wrist  we  counted  eight  carpal  bones,  and  in 
the  ankle  seven  tarsal  bones.  During 
childhood,  however,  the  heel  bone  consists 
of  two  separate  bones ;  hence  until  about 
the  fourteenth  year  both  wrist  and  ankle 
have  eight  separate  bones. 

5.   STRUCTURE  OF  BONES  l 

In  the  skeleton  of  vertebrates  there  are 
two  different  types  of  bone  structure.  One 
type  can  be  studied  to  good  advantage 
from  a  soup  bone ;  the  other  is  well  shown 
in  a  rib  of  lamb  or  beef.  Since  the  latter 
is  the  simpler,  it  will  be  discussed  first. 

Structure  of  a  Rib.  —  After  the  meat  or 
muscle  has  been  removed  from  a  lamb 
chop,  there  remains  a  slender,  curving 
bone,  flattened  in  form,  which  is  the  rib. 
A  piece  of  vertebra  often  remains  con- 
nected with  the  thicker  end  (compare 
with  Fig.  69).  When  the  rib  is  carefully 
separated  from  the  vertebra,  the  two  sur- 
faces that  move  on  each  other  are  found 
to  be  covered  with  smooth,  bluish-white 
cartilage ;  this  lessens  friction. 

If  the  point  of  a  penknife  be  pushed 
into  the  side  of  the  rib,  a  thin  membrane 
of  tough  connective  tissue  can  be  raised 
from  the  outside  of  the  bone  and  pulled 
off  in  sheets.  This  is  the  per-i-os'te-um 
(Greek  pen'  =  around  -f-  oste'on  =  bone). 
The  periosteum  is  of  great  importance  in 
connection  with  the  growth  of  bone,  since 
most  of  the  new  bone  is  formed  just  be- 
neath this  layer  of  connective  tissue,  and 
by  its  agency. 
"Laboratory  Exercises,"  No.  30. 


FIG.  73.  —  Long 
Bone  (Femur). 

A  =  rounded  head 
which  fits  into  sock- 
et of  hip  bone. 

G'=  shaft  of  bone. 

D,  E=  rough  pro- 
cesses to  which  mus- 
cles are  attached.- 

F  =  smooth  sur- 
face of  head  which 
articulates  with  the 
tibia. 


A   STUDY  OF  THE   SKELETON 


175 


The  structure  of  the  bone  itself  is  best  seen  in  cross  and 
longitudinal  sections.  On  the  outside  is  a 
layer  of  compact  hard  bone,  that  cannot  be 
cut  or  dug  out  with  the  point  of  a  knife. 
The  whole  interior  of  the  rib  is  made  up 
of  spongy  bone  (compare  Fig.  74,  1,  2),  the 
spaces  in  the  bone  tissue  being  filled  with  a 
soft  substance  called  red  marrow.  Hence, 
in  cutting  to  the  center  of  a  rib,  one  would 
meet  successively  periosteum,  hard  bone, 
and  spongy  bone  with  its  red  marrow. 

Structure  of  a  Soup  Bone.  — A  soup  bone  is 
more  or  less  cylindrical  in  form,  with  an  en- 
largement at  either  end  (compare  with  Figs. 
73  and  74).  The  longer  central  portion 
is  called  the  shaft,  and  the  enlarged  extremi- 
ties are  known  as  the  heads  of  the  bone. 
The  surface  of  each  head  is  covered  with 
cartilage  wherever  it  moves  upon  another 
bone,  as  was  the  case  with  the  rib.  The 
rest  of  the  head  and  shaft  is  incased  in 
periosteum.  A  longitudinal  section  shows 
the  internal  structure  to  be  as  follows: 
All  over  the  outside  is  found  a  layer  of 
hard  bone  which  is  thick  in  the  shaft  region 
and  relatively  thin  beneath  the  cartilage  of  ' 
the  heads  (compare  with  Fig.  74).  The 
interior  of  the  heads  is  largely  composed 
of  spongy  bone.  The  long  central  cavity  of 
the  shaft  is  filled  with  fatty  yellow  marrow. 

On  comparing  the  rib  and  soup  bone,  we 
see  that  the  marrow  in  the  former  is  found 
only  in  spongy  bone ;  in  the  latter  it  occurs 
in  the  spongy  bone  of  the  heads,  and  in  a 
solid,  fatty  mass  in  the  marrow  cavity  of 
the  shaft. 


^G.  74.  —  Longitu- 
dinal Section  of 
Tibia. 

spongy  bone 
in  heads. 

3  =  hard  bone  in 

shaft. 

4  =  marrow  cav- 

ity in  shaft. 

5  =  layer  of  car- 

tilage     in 


6  =  periosteum 
c  overing 
outside. 

7=  surface  of 
heads  cov- 
ered with 
cartilage. 


176 


STUDIES  IN  PHYSIOLOGY 


Advantages  of  Hollow  Bones.  —  In  the  bone  structure  we 
have  just  described,  two  advantages  are  combined,  namely, 
lightness  and  strength.  The  framework  of  a  bicycle  best 
illustrates  the  principle  involved,  which  is  that  the  greatest 

possible  strength  and  lightness 
are  secured  in  a  given  amount 
of  material  by  using  hollow  cyl- 
inders. The  spongy  bone  within 
the  hard  outside  layer  strength- 
ens still  further  the  bony  cylin- 
der without  adding  greatly  to  the 
body  weight. 

Blood  Supply  in  Bones.  —  In 
the  periosteum  and  throughout 
the  hard  and  spongy  bone  and  the 
marrow  run  numerous  blood  ves- 
sels that  bring  the  proteid  and 
other  food  materials  required  for 
the  nutrition  of  the  living  bone 
cells.  From  the  blood,  also,  these 
cells  take  out  the  various  mineral 
matters  needed  to  form  the  hard 
intercellular  substance,  which 

gives  to  bone   its  rigidity.     We 

The  branching  tubes  are  canals    £  ,    ,    *      .  J   ,   ,  , 

through  which  run  blood  ves-  have  already  noted  the  fact  that 
seis.  The  irregular  black  new  red  corpuscles  are  produced 
spots  represent  the  outlines  of  •  ,1  _,  TnflT.rftw  nf 

] 


FIG.  75.  — A  Longitudinal 
tion  of  Bone  X  200. 


living  bone  cells.    The  white 

portions  of  the  figure  show       Classification    of   the  Bones   of 

the    bony    intercellular    sub-    the  Human    Skeleton.  —  For    COn- 
stance  (compare  with  Fig.  8). 

venience,  the   bones  of  the   hu- 

man skeleton  are  divided  into  four  groups.  In  the  first 
group  are  the  long  bones,  the  humerus,  radius,  ulna,  femur, 
tibia,  fibula,  metacarpals,  metatarsals,  and  the  phalanges  of 
fingers  and  toes.  All  these  bones  have  a  structure  similar 
to  that  of  the  soup  bone  just  described,  in  that  they  have 
two  heads  and  a  shaft,  and  a  central  cavity  filled  with  yel- 


A   STUDY  OF  THE   SKELETON  177 

]ow  marrow.  Long  bones  are  found  in  the  limbs,  where  a 
considerable  range  of  motion  is  desired. 

A  second  group  includes  the  so-called  short  bones,  namely, 
the  carpals,  .tarsals,  and  the  kneecaps.  Short  bones  are 
more  or  less  cubical  in  form,  and  in  structure  resemble  the 
head  region  of  a  long  bone.  Much  of  the  outside  surface  is 
covered  with  cartilage ;  within  is  a  thin  layer  of  hard  bone ; 
while  the  central  portion  is  composed  of  spongy  tissue. 
The  short  bones  glide  over  each  other,  and  so  allow,  in  wrist 
and  ankle,  a  considerable  range  of  motion  in  a  great  many 
directions. 

The  group  of  flat  bones  includes  all  those  that  are  like  the 
rib  in  form  and  internal  arrangement.  They  are  the  ribs, 
breastbone,  collar  bones,  shoulder  blades,  hip  bones,  and  most 
of  the  bones  forming  the  top  and  sides  of  the  cranium. 
Their  principal  function  is  either  that  of  furnishing  pro- 
tection for  the  brain  and  organs  of  the  chest,  or  that  of 
supplying  a  means  of  attachment  of  the  arms  and  legs  to 
the  rest  of  the  skeleton.  In  most  cases  flat  bones  have  little 
or  no  movemento 

Finally,  the  irregular  bones  include  all  those  that  do  not 
readily  fall  into  the  groups  already  enumerated.  As  exam- 
ples may  be  mentioned  the  bones  of  the  spinal  column,  in- 
cluding sacrum  and  coccyx,  the  sphenoid,  ethmoid,  and  the 
bones  of  the  face.  Some  of  them  serve  as  support  (verte- 
brae), others  protect  the  eyes,  ears,  and  nose,  while  in  the 
case  of  the  lower  jawbone  and  the  atlas  vertebra  a  consider- 
able range  of  motion  is  possible. 

6.   CHEMICAL  COMPOSITION  OP  BONE* 

Effect  of  Burning  Bones.  —  Bones,  we  have  found  (p.  27), 
consist  of  two  kinds  of  material :  (1)  the  living  bone  cells 
that  provide  for  the  growth  and  repair  of  bone  tissue,  and 
(2)  the  hard  intercellular  mineral  matter  (see  Figs.  8  and 

1  See  "Laboratory  Exercises,"  No.  31. 

M 


178  STUDIES  IN  PHYSIOLOGY 

75).  The  living  tissue  and  the  fatty  marrow  are  easily 
removed  by  placing  the  bone  in  a  hot  fire.  As  the  bone 
burns,  it  gives  off  the  familiar  smell  that  is  characteristic  of 
proteid,  and  a  black  color  appears,  which  demonstrates  the 
presence  of  carbon.  If  the  flame  is  hot  enough,  the  carbon 
is  oxidized,  and  a  white,  brittle  substance  is  left,  which 
preserves  perfectly  the  form  of  the  bone.  The  marrow 
cavity  is,  however,  completely  empty,  and  in  the  burned 
bone  the  porous  character  of  the  spongy  tissue  becomes 
more  evident. 

By  weighing  the  bone  before  and  after  the  experiment, 
one  demonstrates  that  one  third  of  the  weight  has  disap- 
peared ;  this  of  course  means  that  a  third  is  animal  matter, 
and  the  remaining  two  thirds  mineral  matter.  A  bone  that 
has  been  burned  is  very  brittle,  and  so  the  experiment  like- 
wise proves  that  the  toughness  and  elasticity  of  bone  are 
due  to  the  presence  of  animal  ingredients. 

Action  of  Acid  on  Bones.  —  In  our  study  of  digestion  we 
learned  that  insoluble  mineral  substances  are  dissolved  by 
the  hydrochloric  acid  of  the  gastric  juice.  Hence,  the  hard 
parts  of  bone  can  be  removed  by  the  action  of  this  acid. 
A  rib  bone  that  has  been  soaked  in  diluted  hydrochloric 
acid l  for  several  days  loses  most  of  its  rigidity,  and  while 
retaining  its  shape,  becomes  very  elastic  and  flexible.  To 
the  mineral  ingredients,  therefore,  bone  owes  its  hardness 
and  rigidity  for  supporting  the  weight  of  the  body. 

Nutritive  Ingredients  found  in  Bones.  —  When  pieces  of  large 
soup  bones  are  placed  in  water  and  heated  slowly  (on  the 
back  of  the  stove)  for  several  hours,  a  thick  gelatinous  mass 
is  formed.  This  is  called  soup  stock.  It  contains  most  of 
the  fats,  proteids,  and  other  nutritive  ingredients  of  bones, 
and  with  the  addition  of  vegetables  and  various  condiments 
makes  a  nutritious  and  palatable  soup.  Bones,  therefore, 
should  not  be  regarded  as  refuse  until  after  this  nutrition 
has  been  extracted. 

1  One  part  acid  to  six  parts  of  water. 


A  STUDY   OF  THE   SKELETON 


179 


caps 


7.     A  STUDY  OF  JOINTS 

Definition  of  a  Joint.  —  Thus  far  we  have  considered  the 
bones  of  the  skeleton  as  though  they  were  independent  of 
each  other.  In  the  living 
body,  however,  we  know 
that  they  are  firmly  attached 
to  one  another,  and  that 
thus  a  strong  but  movable 
framework  is  formed.  Any 
region  in  the  skeleton  where 
motion  is  possible  between 
two  bones  is  catted  a  joint. 

Structure  of  a  Leg  Joint  of 
Lamb.1  —  Certain  tissues  are 
always  present  in  a  joint, 
and  most  of  them  can  be 
easily  seen  in  a  leg  joint  of 
lamb  or  veal.  In  the  first 
place,  it  is  clear  that  in  the 
formation  of  a  joint  there 
must  be  at  least  two  sepa-  FlQ 
rate  bones  (compare  with 
Fig.  76).  We  find  in  the  leg 
joint  which  we  are  study- 
ing that  the  bones  are 
bound  tightly  to  one  another 
by  tough  bands  of  connec- 
tive tissue  called  lig'a-ments 
(Latin  ligare  =  to  bind), 
and  that  motion  is  possible 
in  only  two  directions,  like  the  movement  of  a  door  on 
a  hinge.  When  we  studied  the  structure  of  a  long  bone, 
we  found  a  layer  of  cartilage  covering  the  heads  where- 
ever  any  motion  upon  another  bone  took  place,  and  on 

1  See  "Laboratory  Exercises,"  No.  35. 


fil- 


Section    of 
Kneejoint. 

cartilage  on  end  of  tibia, 
connective    tissue    forming    a 

capsule  about  joint. 
e  =  tendon  of  extensor  muscle. 
fern  =  section  of  femur. 
Jib  =  fibula. 
I  =  ligaments  between  femur  and 

tibia. 

pat  =  section  of  patella  (kneecap). 
tib  =  tibia  in  calf  of  leg. 


c 
caps 


180 


STUDIES  IN  PHYSIOLOGY 


cutting  away  the  ligaments  of  this  joint  we  see  the  smooth 
surfaces  of  cartilage.  Bet  ween' them  is  a  slimy  liquid  some- 
thing like  the  raw  white  of  egg.  This  is  the  syn-o'vi-al 
fluid,  which  is  secreted  by  the  synovial  membranes,  that 
cover  the  inner  surfaces  of  the  ligaments,  and  it  serves  to 
lubricate  the  heads  of  the  bones,  and  to  prevent  friction. 
In  its  appearance  and  chemical  composition,  the  synovial 
liquid  resembles  more  or  less  closely  the  blood  serum, 

from  which  it  is 
prepared  by  the 
synovial  membrane. 
Besides  the  liga- 
ments which  join 
the  bones,  one  sees 
other  cords  of  con- 
nective tissue  called 
ten'dons.  A  tendon 
is  attached  at  one 
end  to  a  bone,  and 
at  the  other  end  it 
becomes  continuous 
with  masses  of  mus- 
cle. By  this  means 
the  pull  of  the  mus- 
cle causes  the  move- 
ment of  the  bone. 
The  tissues  we  have  enumerated  are  present  in  the  struc- 
ture of  each  joint  in  the  human  body.  A  joint,  then,  must 
have  (1)  at  least  two  separate  bones,  (2)  layers  of  cartilage, 
(3)  ligaments,  (4)  synovial  membranes  secreting  synovial 
fluid,  (5)  muscles  and  tendons. 

Classification  of  Joints.1  —  The  joints  in  the  human  body 
may  be  divided  into  four  classes,  which  are  as  follows: 
(1)  ball-and-socket,  (2)  hinge,  (3)  gliding,  (4)  pivot. 

A  ball-and-socket  joint,  as  the  name  implies,  is  formed  be- 
i  See  "  Laboratory  Exercises,"  No.  36. 


FIG.  77.  —  Connective  Tissue  Fibers. 

a  =  small  bundles  of  fibers. 
b  =  larger  bundles  of  fibers. 
c  =  single  elastic  fibers. 


A  STUDY  OF  THE   SKELETON  181 

tween  the  more  or  less  spherical  head  of  a  long  bone  and  a 
cup-shaped  cavity  in  another  bone.  The  best  examples  of 
this  sort  of  joint  are  found  at  the  shoulder  and  at  the  hip. 
Great  freedom  of  movement  is  possible  in  a  ball-and-socket 
joint.  The  arm  can  be  moved  upon  the  shoulder  blade 
(1)  backward  and  forward  in  a  quarter  circle  at  the  side  of 
the  body,  i.e.  flexed  and  extended,  (2)  outward  or  inward  in 
a  circle  in  front  (ab-duct'ed  and  ad-duct- ed),  (3)  the  whole  arm 
when  held  stiff  may  be  made  to  describe  a  cone  (cir'cum- 
duct'ed),  and  (4)  it  may  be  twisted  in  the  socket  (ro'ta-ted). 
A  much  greater  range  of  movement  than  that  just  de- 
scribed is  made  possible  for  the  arm  by  the  fact  that  the 
bones  of  the  pectoral  girdle  are  loosely  attached  to  the 
rest  of  the  skeleton,  and  hence  can  move  with  the  arms. 
The  hip  joint  allows  all  four  of  the  movements  enumerated 
above,  but  the  amount  of  motion  is  less,  since  the  hip  socket 
is  much  deeper,  and  since  the  pelvic  bones  are  closely  at- 
tached to  the  sacrum.  Other  ball-and-socket  joints  are 
found  between  the  metacarpals  and  phalanges  of  the  hand 
and  between  the  metatarsals  and  phalanges  of  the  foot. 

We  have  become  familiar  with  the  structure  of  a  hinge 
joint  in  our  study  of  the  leg  of  a  sheep.  Motion  is  possible 
in  but  two  directions.  When  the  joint  is  moved  so  that  the 
two  bones  form  an  angle  with  each  other,  the  joint  is  said  to  be 
flexed;  if  the  bones  are  made  to  form  a  straight  line,  the  joint  is 
extended.  Following  is  a  list  of  the  hinge  joints  of  the  body:  — • 

REGION  OF  JOINT  JOINT  OCCURS  BETWEEN 

elbow  humerus  and  ulna  -f-  radius, 

wrist  carpals  and  metacarpals. 

fingers  the  different  phalanges, 

knee  femur  and  tibia, 

ankle  tibia  -f-  fibula  and  tarsals. 

toes  the  different  phalanges, 

head *  lower  jaw  and  temporal, 

neck  skull  and  atlas. 

i  This  joint  also  belongs  to  the  class  of  gliding  joints. 


182  STUDIES  IN  PHYSIOLOGY 

The  third  class  includes  the  gliding  joints,  and  these  are 
usually  formed  of  short  bones.  They  glide  over  each  other 
in  several  directions  and  so  allow  a  small  range  of  move- 
ment in  many  directions. 

KBGION  OF  JOINT  JOINT  OCCURS  BETWEEN 

wrist  radius  and  carpals. 

wrist  the  different  carpals. 

knee  kneecap  and  the  femur, 

arch  of  foot  the  different  tarsals  and  tlie 

metatarsals. 

head  (both  hinge  and  lower  jaw  and  temporal. 

gliding) 

spinal  column  the  different  vertebrae, 

chest  region  vertebrae  and  ribs. 

In  SL  pivot  joint  one  bone  moves  around  a  projection  of  the 
other,  the  latter  serving  as  a  pivot.  Such  a  joint  is  formed 
between  the  first  two  vertebrae  (see  Fig.  67).  The  peg  of 
the  axis,  projecting  upward  through  a  hole  in  the  atlas,  is 
the  pivot  about  which  the  atlas  'turns.  A  rather  more  com- 
plicated kind  of  pivot  joint  is  formed  between  the  radius  and 
a  lower  process  of  the  humerus.  The  action  of  this  joint 
is  easily  demonstrated  in  the  following  manner:  Extend 
the  forearm  and  the  hand  on  the  table  with  the  palm  up ; 
then,  without  lifting  the  elbow  from  the  table,  turn  the 
hand  over,  so  the  palm  is  downward.  In  this  movement 
the  lower  (distal)  end  of  the  radius  crosses  the  ulna,  carry- 
ing the  hand  along  with  it  (see  Fig.  78).  It  is  because  of 
this  rotating  motion  that  the  radius  bone  has  received  its 
name. 

8.   THE  HYGIENE  OF  THE  SKELETON 

Food  and  the  Skeleton.  —  In  the  composition  of  bones,  we 
found  two  kinds  of  matter,  namely,  animal  and  mineral. 
For  the  growth  of  bones,  therefore,  it  is  essential  that  there 
be  a  supply  of  both  of  these  building  materials.  Bone  cells, 


A   STUDY   OF   THE   SKELETON 


183 


like  all  other  protoplasm,  require  proteid  and  water;  the  fats 
and  carbohydrates  of  food  are  probably  converted  into  fatty 
marrow;  while  the  intercellular  substance  is  formed  from 
the  mineral  matters  brought  by  the  blood.  Milk  is  a  most 
important  article  of  diet  in 
early  life,  since  in  addition  to 
the  other  nutrients,  it  supplies 
the  phosphate  of  lime  needed 
for  bone  manufacture.  In  the 
process  of  refining  wheat  flour 
much  of  the  mineral  matter  is 
lost;  for  this  reason  whole 
wheat  flour  and  the  coarser 
cereals  like  corn,  rye,  and  oats 
are  much  more  valuable  as 
bone  builders,  and  are  espe- 
cially needful  during  the  period 
of  growth.  The  insoluble  min- 
eral matters  in  these  foods  are 
made  soluble  by  the  gastric 
juice  in  the  stomach.  The 
soluble  salts  are  then  supplied 
by  the  blood  to  the  bone  cells, 
and  these  in  turn  convert  this 
mineral  matter  into  the  hard 
intercellular  substance. 

Effect  of  Pressure  on  Bones.  — 
Tight-fitting  clothing  is  a  most 
important  factor  in  modifying 
permanently  the  shape  and  po- 
sition of  bones.  Normal  growth  cannot  be  attained  if 
the  skeleton  is  subjected  to  pressure.  Yet  this  important 
principle  of  hygiene  is  constantly  violated  by  women  who 
wear  tight-fitting  clothing  about  the  waist.  Baneful  fashion 
is  often  followed  even  in  youth,  when  the  skeleton  yields 
readily  to  pressure.  The  result  is  that  the  ribs  are  perma- 


FIG.  78.  —  Pivot  Joint  of  Right 
Arm. 

A  =  position  of  bones  when  back 

of  hand  is  down. 
B  =  position  of  bones  when  palm 

of  hand  is  down. 
H=  humerus. 
R  =  radius. 
U  =  ulna. 


184 


STUDIES  IN  PHYSIOLOGY 


nently  bent  inward  toward 'the  breastbone,  thus  interfering 
seriously  with  the  action  of  the  abdominal  organs.  High- 
heeled  shoes  are  another  frequent  cause  of  deformity. 
They  reduce  the  spring  in  the  arch  of  the  foot  and  throw 
too  much  of  the  weight  of  the  body  upon  the  tips  of  the 
toes.  Shoes  with  narrow  toes  should  never  be  worn. 


FIG.  79.  —Effect  of  Tight  Lacing  on  the  Organs  of  Chest 
and  Abdomen. 


A  =  normal  position  of  organs. 


B  =  position  of  organs  after  lacing. 


9.   ACCIDENTS  TO  THE  SKELETON 

Fractures. — Any  sudden  strain  or  blow  upon  a  bone  is 
liable  to  cause  a  break  or  &  fracture,  especially  in  later  life, 
when  the  bones  are  brittle.  If  the  bone  is  broken  into  but 
two  pieces,  the  accident  is  described  as  a  simple  fracture  ; 
when  several  breaks  occur,  it  is  called  a  splintered  fracture  ; 
and  if  the  pieces  of  bone  work  out  into  or  through  the  flesh, 
a  compound  fracture  results.  Fractures  occur  more  com- 
monly in  the  shafts  of  long  bones,  and  they  can  usually  be 
recognized  by  the  fact  that  an  extra  joint  is  thus  formed  and 
by  the  fact  that  the  broken  ends  grate  against  each  other. 

In  treating  a  fracture,  the  pieces  of  bone  must  be  brought 


A   STUDY   OF  THE   SKELETON  185 

back  into  position  (this  is  called  "  setting "  the  bone),  and 
must  be  held  in  place  by  splints  until  the  ends  have  become 
firmly  "knit"  together.  Unless  it  is  impossible  to  secure 
surgical  assistance  within  a  day  or  two,  the  setting  of  a 
bone  should  never  be  attempted  by  one  who  is  not  familiar 
with  the  skeleton.  In  general  but  two  rules  should  be  fol- 
lowed in  case  of  a  fracture :  ftrst,  send  for  a  doctor;  second, 
keep  the  broken  bone  perfectly  quiet  in  as  comfortable  a  posi- 
tion as  possible.  Cold  water  applications  often  reduce  the 
pain  and  prevent  inflammation.  Movement  at  the  point 
of  fracture  almost  always  causes  inflammation,  which  makes 
the  setting  difficult ;  and  if  moved  suddenly,  a  simple  break 
may  become  a  compound  fracture. 

Dislocations. — A  dislocation  is  an  accident  to  a  joint 
in  which  the  ends  of  the  bones  are  forced  apart.  One  can 
usually  recognize  a  dislocation  by  the  unwonted  protrusion 
of  the  bones,  and  by  the  pain  caused  when  any  motion  at  the 
joint  is  attempted.  Since  the  ligaments  bind  the  bones  to- 
gether rather  closely,  a  dislocation  often  results  in  a  wrench- 
ing or  tearing  of  the  connective  tissue  about  a  joint ;  swelling 
and  discoloration  follow  quickly ;  and  it  is  therefore  neces- 
sary to  put  the  bones  back  into  place,  or,  in  other  words,  to 
"reduce  the  dislocation"  as  soon  as  possible.  If  .surgical 
aid  can  be  procured,  it  is  better  to  apply  cold  water  to  the 
joint  and  wait  for  the  doctor's  arrival,  since  by  unskillful 
treatment  further  injury  to  the  joint  may  result.  When 
skilled  treatment  is  impossible,  most  dislocations  can  be 
reduced  by  steadily  pulling  the  bones  apart  until  it  is  possi- 
ble for  the  ends  to  glide  back  into  place. 

Sprains.  —  When  a  sudden  strain  causes  neither  a  fracture 
nor  a  dislocation,  it  often  gives  rise  to  a  twisting  or  tearing 
of  ligaments  and  tendons  in  the  region  of  a  joint.  Such  an 
accident  is  called  a  sprain.  The  injured  region  is  usually 
swollen  and  painful.  Since  it  is  difficult  to  distinguish  a 
sprain  from  other  accidents  to  the  skeleton,  medical  assist- 
ance should  be  summoned  and  the  following  directions  care- 


186  STUDIES  IN  PHYSIOLOGY 

fully  followed :  (1)  the  sprained  member  should  be  placed 
at  once  into  cold  water  or  into  hot  water  and  held  there  for 
some  time ;  (2)  it  should  meanwhile  be  rubbed  as  vigorously 
as  possible  without  causing  pain ;  (3)  arnica,  Pond's  extract, 
or  some  other  "  pain  killer "  should  be  applied  ;  (4)  the 
sprain  should  then  be  bound  in  a  tight  bandage  (these  four 
applications  tend  to  keep  down  the  swelling)  ;  and  (5)  (most 
important  of  all)  the  joint  should  have  complete  rest  until  all 
swelling  and  soreness  have  disappeared.  It  is  probable  that 
more  permanent  injuries  result  from  careless  treatment  of 
sprains  than  from  all  other  accidents  to  the  skeleton. 

10.   A  COMPARATIVE  STUDY  OF  SKELETONS1 

Skeletons  of  Invertebrates  and  of  Vertebrates.  —  We  have 
defined  a  vertebrate  as  an  animal  with  a  backbone,  and  an 


FIG.  80.  —Living  Coral  surrounded  by  its  Outer  Skeleton. 

invertebrate  as  an  animal  without  a  backbone.  This  dis- 
tinction between  the  two  subdivisions  of  the  animal  king- 
dom can  be  carried  still  farther,  and  we  may  say  that  in 
general  the  invertebrates  either  have  no  skeleton  at  all  or 
that,  when  present,  the  skeleton  is  on  the  outside  of  the 

1  See  "Laboratory  Exercises,"  No.  37. 


A  STUDY  OF  THE   SKELETON  187 

body;  whereas  vertebrates  are  characterized  by  the  pos- 
session of  a  bony  skeleton  within  the  body.  There  are, 
however,  exceptions  to  this  general  rule. 

Invertebrate  Skeletons. — Most  of  us  are  familiar  with  com- 
mon coral  in  its  branching  form  or  in  the  spherical  form 
which  resembles  the  human  brain  (Fig.  80).  This  coral 
is  really  a  skel- 
eton formed  by 
coral  animals 
as  a  means  of 
protection.  The 
depressions  in 
the  surface  of 
the1  skeleton  in- 
dicate the  posi- 
tion and  form 
of  the  bodies 
of  the  animals. 
Starfishes,  too, 
construct  a  cov- 
ering of  bony 
plates  in  the 
skin  which,  al- 
though hard  FIG.  81.— Living  Starfish,  showing  Tube  Feet  pro- 
'  jecting  from  the  Lower  Surface  of  the  Skeleton. 
can  be  moved  The  Mouth  is  in  the  Center  of  the  Star, 
by  the  living 

animals  (Fig.  81).  The  outside  skeleton  of  the  mollusks 
(snails  and  clams)  takes  the  form  of  a  single  or  double 
shell,  within  which  the  animal  can  withdraw  itself,  and 
oftentimes  completely  close  the  shell. 

On  the  exterior  of  the  body  of  lobsters,  crayfishes,  and  of 
most  insects  is  a  hard  covering  that  incloses  the  soft  parts. 
As  the  animal  grows,  the  shell  becomes  too  small,  and  then 
it  is  split  along  the  dorsal  surface.  The  animal  then  pulls 
its  body  out  of  the  shell  and  withdraws  to  a  protected  place 
until  a  new  hard  skeleton  is  formed.  One  might  compare 


188  STUDIES   IN   PHYSIOLOGY 

this  means  of  protection  of  these  crus-ta'cea  (Latin  crusta  = 
the  hard  surface  of  a  body),  to  that  afforded  by  a  coat  of 
mail  worn  by  the  warriors  of  the  middle  ages.  This  com- 
parison is  more  striking  since  some  of  the  plates  of  this 
outside  skeleton  move  over  each  other  at  the  joints  in  a 
manner  similar  to  the  iron  plates  of  the  armor  (Fig.  82). 

Vertebrate  Skeletons.  —  It  would  be  impossible  to  give  in  a 
limited  space  any  extended  account  of  the  skeletons  of  the 


FIG.  82.  — The  Crayfish,  showing  Hard  Exo-skeleton. 

various  groups  of  vertebrates.     A  few  facts  may  be  noted, 
however. 

We  have  learned  that  the  skeleton  of  a  young  child  is 
first  formed  of  cartilage;  some  of  the  fishes  (sharks  and 
sturgeon)  possess  a  cartilaginous  skeleton  throughout  life. 
In  all  of  the  vertebrates,  with  the  exception  of  the  snakes 
(and  a  few  rare  lizards  and  amphibia),  we  find  anterior  ap- 
pendages that  correspond  to  the  arms  of  man,  and  posterior 
appendages  corresponding  to  legs.  Both  sets  of  these 
appendages  are  used  by  fishes  in  swimming;  the  posterior 
limbs  of  a  frog  are  employed  in  jumping  and  swimming; 
while  in  birds  the  anterior  appendages  are  of  use  in  flying. 


A   STUDY   OF  THE   SKELETON 


189 


In  spite  of  these  great  differences  in  form  and  function,  we 
find  in  each  appendage  bones  that  correspond  to  some  or  all 
of  those  in  the  human  arm  and  leg  (compare  Fig.  83). 

Frogs  have  a  breastbone,  but  no  well-defined  ribs ;  snakes 
have  ribs  the  whole  length  of  the  body  (sometimes  several 


FIG.  83.  —  Skeleton  of  the  Frog. 
Carp  =  carpal  bones  (6) . 


II,  Pit  =  pelvic  girdle. 
R,  U  =  radio-ulna. 


Cor,  Cl,  Sc  =  pectoral  girdle. 
Fe  =  femur. 

Tarsi,  Tibl,  Fiblr  =  tarsal  bones  (5). 
Ti  +  Fi  =  tibio-fibula. 
F1  =  first  vertebra. 
FK  =  ninth  vetebra. 

/'  =  rudiment  of  sixth  toe. 
I,  II,  III,  IV,  V  =  metacarpals  and  metatarsals. 

hundred  pairs),  but  have  no  breastbone.  In  addition  to 
their  inside  skeleton,  turtles  have  thick  shells  which  are  on 
the  outside  like  the  skeleton  of  an  invertebrate  (see  p.  245). 
In  birds  most  of  the  bones  are  hollow  and  filled  with  air,  an 
arrangement  that  helps  to  give  to  these  animals  some  of 
their  buoyancy  in  flying. 


190 


STUDIES   IN  PHYSIOLOGY 


~£one 


Anterior  Appendages  of  Mammals.  —  In  the  single  group  of 
mammals  we  find  most  striking  variations  in  the  form  and 
functions  of  anterior  appendages. 
One  would  expect  to  find  little  in 
common  in  the  structure  of  a  bat's 
wing,  a  seal's  fin,  a  giraffe's  front  leg, 
and  a  lion's  paw.  Yet  in  all  these 
appendages  there  is  a  single  humerus, 
a  radius,  an  ulna,  and  a  number  of 
carpals,  metacarpals,  and  phalanges. 
Equally  interesting  is  a.  comparison 
of  the  use  made  by  mammals  of  the  digits  or  fingers  of  the 
anterior  limb.  Bears  walk  on  the  palm  of  the  hand  and 
hence  are  called  flat-footed.  Elephants  rest  their  weight  on 
the  under  surface  of  four  of  the  five  digits.  The  rhinoceros 


FIG.  84.  —  Sectional  View 
of  Foot  of  Horse. 


Cranium 


Azit 

-^•-Cervical  Vertebra*  ( 7) 


Carpal 
JUeto&trjMl  Banes 


FIG.  85.  —  Skeleton  of  the  Horse. 


has  three  fingers  or  three  toes  on  each  appendage.     In  cows, 
deer,  and  sheep  we  find  but  two  fingers  on  each  front  foot, 


A   STUDY   OF  THE   SKELETON 


191 


on  the  tips  of  which  the  weight  of  the  body  is  supported. 
Finally,  horses  have  but  a  single  digit  on  each  foot,  the  end 
bone  of  which  is  covered  with  the  hoof  (Fig.  84). 

The  story  of  the  horse,  as  it  is  learned  from  the  fossil 
bones  obtained  from 
the  rocks,  is  an  in- 
teresting one.  The 
earliest  horse  of 
which  we  know  any- 
thing was  about  the 
size  of  a  fox,  and 
walked  on  the  dis- 
tal part  of  four  fin- 
gers of  each  front 
foot  and  of  three 
hind  toes,  all  of 
about  equal  size. 
Gradually,  how- 
ever, the  descend- 
ants of  this  animal 
came  to  walk  more 
and  more  on  the 
tips  of  the  middle 
fingers  and  the  mid- 
dle toes.  The  little 
fingers  were  there- 
fore too  short  to 
touch  ground,  they 
became  smaller  as 
the  ages  passed,  and 
have  altogether  dis- 


Fore  Foot 

Hind  Foot 

S      One  Toe 

, 

3 

7      One  Toe 

Splints  of 
2-^nd  4*d\$ts 

< 

Splints  of 
•j     2"J8nd  4*di£f» 

% 

S    Three  Toes 

Three  Toes 

5ide  toes 

Side  toes 

nottouchingtheground 

not  touching  the  ground 

f    Three  Toes 

Side  toes 
touching  the  ground; 
splint  of  5*  digit 

J 

) 

Three  Toes 

Side  toes 
touching  the  ground 

u 

U     Four  Toes 

fFour  Toes 

H       Three  Toes 

ill     Splint  of  5&di$t. 

Splint  of  1'-'  digit 

FIG.  86.  —  The  Development  of  the  Fore  and 
Hind  Feet  of  a  Horse.  Feet  of  Modern  Horse 
are  figured  at  the  Top.  —  From  diagram  in 
American  Museum  of  Natural  History. 


appeared  in  the  modern  horse.  As  the  middle  digit  came  to 
be  used  more,  its  size  notably  increased,  while  there  was  a 
corresponding  decrease  in  the  size  of  the  digits  on  either  side. 
In  skeletons  of  horses  that  lived  nearer  modern  times,  we  lose 
all  trace  of  the  phalanges  of  these  two  side  digits,  and  in  the 


192  STUDIES  IN  PHYSIOLOGY 

horse  of  to-day  there  is  nothing  to  suggest  this  long  story 
with  the  exception  of  two  so-called  splint  bones  along  the 
sides  of  the  lower  leg ;  these  are  the  remains  of  the  two  meta- 
carpal  bones  to  which  the  two  side  fingers  were  attached. 

Peculiarities  of  the  Human  Skeleton.  —  In  the  human  body 
there  is  no  bone  or  set  of  bones  that  is  not  found  in  varied 
form  in  all  the  mammals  and  in  most  other  vertebrates; 
indeed  so  far  as  we  can  learn  from  the  structure  of  his  skele- 
ton, man  is  much  more  closely  .related  to  the  gorilla  and  the 
chimpanzee  than  are  these  animals  to  the  lower  monkeys. 
Yet  there  are  certain  general  peculiarities  of  form  that  are 
found  in  the  skeleton  of  man  alone,  these  distinctive  charac- 
teristics being  due  in  a  great  degree  to  his  erect  position. 

In  the  first  place,  in  even  the  highest  monkeys  the  length 
of  the  arms  is  nearly  equal  to  that  of  the  legs.  For  while 
the  gorilla  can  walk  on  two  feet,  all  four  appendages  are 
often  employed  in  locomotion.  In  man,  on  the  other  hand, 
the  legs  are  much  longer  than  the  arms,  an  advantage  that 
permits  of  long  strides  in  walking. 

Again,  no  other  animal  has  the  four  curves  in  the  spinal 
column  and  the  arched  instep.  These  provisions  are  more 
necessary  in  man  because  the  head  rests  on  the  top  of  the 
spinal  column,  and  any  sudden  jar  would  be  transmitted  to 
the  brain  were  it  not  for  the  presence  of  these  elastic  springs. 

The  human  skull  is  nearly  balanced  on  the  top  of  the 
spinal  column,  while  that  of  other  animals  is  attached  to  the 
anterior  end  of  a  more  or  less  horizontal  backbone.  Man's 
cranium  is  much  larger  than  the  skeleton  of  the  face,  whereas 
even  in  the  highest  monkeys  the  heavy  face  bones  more  than 
balance  the  bones  of  the  brain-case,  and  thus  it  is  difficult 
for  the  animal  to  hold  its  head  erect  for  any  length  of  time. 

Finally,  the  gradual  increase  in  the  size  of  the  vertebrae 
from  the  neck  to  the  sacrum  and  the  breadth  of  the  pelvis 
(both  characteristics  peculiarly  human)  give  a  stable  base 
on  which  the  erect  trunk  is  supported  by  the  legs. 


CHAPTER   X 
A  STUDY  OF  THE  MUSCLES 

Importance  of  Muscle  Tissue.  —  Muscle  tissue  constitutes 
or  almost  half  of  the  weight  of  the  human  body. 
In  this  kind  of  tissue  is  found  one  fourth  of  all  the 
blood.  But  the  importance  of  muscle  tissue  is  appre- 
ciated, even  more  fully,  when 
we  realize  that  nearly  every 
kind  of  movement  in  the  body 
is  due  to  the  action  of  the 
muscles.  Not  only  do  they 
bring  about  the  more  obvious 
motions  of  the  arms,  the  legs, 
the  trunk,  and  the  head,  but 
also  to  muscular  action  are 
due  all  the  contractions  of  the 
heart,  of  the  stomach,  and  of 
the  other  internal  organs. 
Every  change  in  the  expres- 
sion of  the  face,  and  every 
variation  in  the  tone  of  the 
voice  is  likewise  a  result  of  Fia.ST.-Musdes^of  the  Head  and 
the  action  of  this  all-important 

tissue.  Hence  we  are  not  surprised  that  there  are  over  jive 
hundred  separate  muscles,  which  vary  in  length  from  the 
fraction  of  an  inch  (within  the  ear  cavity)  to  over  a  foot 
and  a  half  (down  the  front  of  the  thigh). 

Kinds  of  Muscle.  —  All  of  these  muscles  are  in  one  way  or 
another  under  the  control  of  the  nervous  system.     Some 
o  193 


194 


STUDIES  IN  PHYSIOLOGY 


of  them  are  directed  by  the  conscious  portions  of  our  brain. 
Thus  we  can  close  our  fingers  and  open  them  as  we  please ; 
we  can  move  the  eyes,  the  head,  and  the  legs  at  will.  We 
call  all  the  muscles  that  are  controlled  by  our  will  power, 
vol'un-ta-ry  muscles  (Latin  voluntas  =  will).  Most  of  the 
muscles  of  the  throat,  those  of  the  gullet,  stomach,  and 
intestines,  on  the  other  hand,  act  without  any  voluntary 
direction  on  our  part,  and  they  are  therefore  called  in-voV- 
un-ta-ry. 

1.    THE  VOLUNTARY  MUSCLES  * 

The  Biceps  Muscle.  —  When  I  place  my  left  hand  on  the 
front  surface  of  my  right  upper  arm,  and  then  draw  up  my 

right  forearm  as 
far  as  possible,  I 
feel  the  muscle 
in  front  of  the 
humerus  become 
shorter,  thicker, 
and  harder.  By 
extending  the 
forearm  again,  a 
tough  cord  or 
ten1  don  can  be 
felt  at  the  lower 
or  distal  end  of 
the  muscle.  This 
tendon  attaches 
the  muscle  to  the 
radius  bone.  The  proximal  end  of  this  muscle  is  covered  by 
thick  layers  of  flesh,  but  if  these  were  removed,  we  should 
find  two  other  tendons,  which  connect  the  muscle  with  pro- 
jections on  the  shoulder  blade  (Fig.  88).  We  are  now  pre- 
pared for  certain  definitions.  The  muscle  we  have  been 
studying  is  called  the  bi'ceps,  from  the  fact  that  its  upper 

iSee  "Laboratory  Exercises,"  No.  33. 


FIG.  88.  —  Action  of  the  Biceps  Muscle. 

a  =  attachment  of  tendons  to  shoulder. 
_?*  =  elbow  point. 

P  =  attachment  of  lower  tendon  to  the  radius. 
W  =  weight  of  the  hand. 


A   STUDY   OF  THE   MUSCLES  195 

end  has  two  heads  or  tendons  (Latin  U  =  two  -f  caput  = 
head).  The  central  portion  or  the  part  that  contracts  is 
called  the  belly  of  the  muscle. 

Since  the  biceps  muscle  is  joined  above  to  the  shoulder 
blade  and  below  to  the  radius,  it  therefore  passes  across 
two  joints.  When  we  lift  a  book  with  our  forearm,  the 
upper  tendons  remain  practically  unmoved ;  this  end  of  the 
muscle  is  then  called  its  origin.  The  tendon  attached  to 
the  radius,  however,  is  made  to  move  considerably,  and  to 
this  end  is  given  the  name  insertion  of  the  muscle.  If,  on 
the  other  hand,  we  climb  a  rope  hand  over  hand,  the  elbow 
joint  is  held  firm,  and  the  motion  takes  place  at  the  shoul- 
der. Under  these  conditions  the  radius  end  is  the  origin, 
and  the  scapular  end  the  insertion.  By  origin  of  a  muscle 
is  meant  the  end  that  moves  least;  by  insertion,  the  end  that 
moves  most.  In  the  majority  of  muscles  one  end  is  always 
origin,  the  other  insertion. 

The  Triceps  Muscle.  —  If  we  straighten  or  extend  the  fore- 
arm as  far  as  possible,  the  belly  of  a  muscle  behind  the 
humerus  is  found  to  swell.  This  is  the  tri'ceps  muscle 
(Latin  tri  =  three  -f-  caput  =  head),  so  called  because  it  has 
three  tendons  at  its  upper  end.  These  tendons  form  the 
origin  of  the  triceps,  and  are  attached  to  the  shoulder  blade 
and  to  the  humerus.  The  insertion  of  the  muscle  is  on  the 
projecting  head  of  the  ulna  (commonly  known  as  the  "  funny 
bone")  (see  Fig.  89). 

Arrangement  of  Muscles  in  the  Body.  —  If  the  biceps  muscle 
is  made  to  contract,  the  forearm  is  brought  upward  or 
flexed.  When  the  triceps  exerts  its  force,  the  biceps  relaxes 
and  the  forearm  is  straightened  or  extended.  This  illus- 
trates the  paired  arrangement  of  muscles  throughout  the 
body ;  for  a  flexor  muscle  on  one  side  of  a  joint  is  bal- 
anced by  an  extensor  on  the  other  side,  which  acts  as  its 
antagonist. 

Along  the  palm  side  of  the  forearm  are  the  bellies  of  the 
flexor  muscles  that  bend  the  fingers,  while  on  the  back  of 


196 


STUDIES  IN  PHYSIOLOGY 


the  radius  and  ulna  are  the  ringer  extensors.  The  origin  of 
each  of  these  sets  of  muscles  is  in  the  region  of  the  elbow 
joint.  Long  tendons,  easily  felt  in  the  wrist  region,  run 
over  the  carpals  and  metacarpals  and  are  attached  to  the 


Extensor*  of  fh«  H»nd  ......_ 


_/lexot$  of  the  Hand 


Ft«»0'«  Of  th*  Foot 


_G«itroenemiu» 


_Tendo  AcriillM 


FIG.  89.  —  Muscles  of  the  Body. 

tips  of  the  various  phalanges.  By  this  arrangement  the 
muscles  that  move  the  ringers  are  placed  up  in  the  forearm 
out  of  the  way,  thus  allowing  a  small  and  graceful  outline 
for  the  hand. 

The  same  pairing  off  of  muscles  is  likewise  seen  in  the  leg 


A   STUDY  OF  THE   MUSCLES  197 

region.  One  muscle  is  especially  developed  in  the  back  of 
the  calf  of  the  leg,  and  is  attached  to  the  heel  bone  by  the 
tendon  of  Achilles  (so  called  because  in  Greek  mythology  the 
hero  Achilles  is  said  to  have  met  his  death  by  an  arrow  that 
pierced  this  tendon).  When  the  extensor  muscle  we  have 
been  describing  contracts,  it  raises  the  body  on  tiptoe  (see 
Fig.  89).  The  corresponding  flexor,  that  causes  one  to  stand 
on  the  heels,  runs  from  the  knee  down  the  front  of  the 
tibia,  its  insertion  being  on  the  ankle  bones. 

In  the  ventral  wall  of  the  abdomen,  in  the  region  of  the 
face,  and  in  some  other  parts  of  the  body,  the  muscles  are 
arranged  in  broad,  flattened  masses  and  serve  as  a  movable 
wall  to  inclose  the  cavities  within.  Like  the  muscles  of  the 
appendages,  they  are  attached  to  the  skeleton  or  to  each 
other  by  tendons. 

Structure  of  Voluntary  Muscle.  —  A  thick  piece  of  steak 
cut  from  a  leg  of  beef  furnishes  good  material  for  the  study 
of  voluntary  muscle.1  One 
sees  that  the  muscle  can  be 
separated  into  rather  large, 
more  or  less  cylindrical  or 
prism-shaped  masses,  that 
run  along  the  leg  bone. 
Each  of  these  masses  is 
called  a  muscle  bundle.  It 
is  surrounded  by  a  tough, 
glistening  sheet  of  con- 
TiPPtivp  ti^np  Pallprl  wr  FlG'  ^-  —  Muscle  Bundles  (/)  bound 

L    Per~      together  to  make  a  Piece  of  Muscle. 
i-my'si-um    (Greek    peri  = 

around  +  mys  =  muscle).  When  this  perimysium  is  pulled 
off,  the  bundle  is  found  to  be  composed  of  smaller  bundles, 
and  each  of  these  is  enveloped  in  a  thin  sheath  of  peri- 
mysium. These  smaller  bundles,  in  turn,  can  be  separated 
still  further  until  one  gets  a  bundle,  or  piece  of  bundle,  so 
small  that  it  can  hardly  be  seen  with  the  naked  eye. 
1  See  "Laboratory  Exercises,"  No.  34. 


198 


STUDIES   IN  PHYSIOLOGY 


FIG.  91.  —  A  Portion  of  Two  Striped 
Muscle  Fibers,  highly  magnified. 
n  =  nucleus. 
s  =  covering  of  fiber. 


If  this  bit  of  muscle  is  put  on  a  glass  slide  in  a  drop  of 
water,  teased  apart  with  needles,  and  examined  with  the 

compound  microscope,  it  is 
found  to  be  composed  of  tiny 
threads  lying  side  by  side,  and 
held  together  by  the  thin  sheet 
of  perimysium.  Each  of  these 
threads  is  a  muscle  fiber.  Close 
examination  shows  that  each 
fiber  is  marked  by  very  minute 
lines  that  run  across  it,  and 
give  it  an  appearance  resem- 
bling that  of  a  very  fine  file. 
Because  of  this  appearance, 
voluntary  muscle  is  also  called 
striped  muscle.  If  the  fibers 
are  properly  stained,  nuclei 
appear  here  and  there,  showing  that  muscle,  like  all  other 
kinds  of  tissue,  is  made 
up  of  cells.  When  a 
muscle  is  made  to  con- 
tract, each  one  of  the 
fibers,  like  the  whole 
muscle,  becomes  shorter, 
thicker,  and  harder. 

Blood  Supply  of  Mus- 
cles.—  Fresh  muscle  is 
deep  red  in  color,  and 
this  is  due  to  the  pres- 
ence of  a  great  quantity 
of  blood.  If  one  finds 
in  the  muscle  the  open-  FlG>  92.  — Blood  Vessels  in  a  Piece  of 
ing  of  a  large  blood  Striped  Muscle,  magnified  150  times. 

vessel  and  forces  into  it,  'cope' 

by  means  of  a  syringe,  a  mixture  of  hot  gelatin  stained  with 
some  coloring  matter,  each  minute  blood  vessel  is  distended, 


A   STUDY   OF  THE   MUSCLES 


199 


and  when  the  gelatin  cools,  the  network  of  blood  vessels  can 
be  traced  to  the  fine  capillaries  that  run  around  the  smaller 
muscle  bundles.  A  microscop- 
ical preparation  shows  still  finer 
branches  between  the  individual 
fibers.  From  the  lymph  that 
comes  from  these  microscopic 
tubes,  each  muscle  fiber  takes  the 
all-important  proteid,  the  sugar, 
fat,  and  water,  and  to  the  lymph  in 
exchange  are  given  the  waste  car- 
bon dioxid,  water,  and  urea  pro- 
duced during  muscular  activity. 

Nerve  Supply  to  Muscles.  —  Much 
of  the  wonderful  progress  in  micro- 
scopical work  that  has  been  made 
in  recent  years,  has  been  due  to 
discoveries  in  methods  of  staining. 
Several  chemical  mixtures  are  now  ?^  1 11 

known  which,  if  applied  to  muscle, 
will  stain  nerve  tissue  in  such  a 
way  that  it  can  be  readily  dis- 
tinguished from  every  other  kind 
of  tissue.  Hence  in  microscopical 
preparations,  it  is  possible  to  trace 
the  minute  branches  of  a  nerve 
from  the  brain  or  spinal  cord, 
through  the  muscle  bundles,  to 
their  endings  on  the  muscle  fibers. 


FIG. 


in 


We  see,  therefore,  that  the  ner- 
vous system  controls  the  action 
not  only  of  a  whole  voluntary 
muscle,  but  also  of  each  individual 
muscle  fiber. 

Standing.  —  Although    to    most 
of   us   it    seems   an   easy   matter 


93.— Muscles    used 
standing  erect. 

I  =  muscles  back  of  calf. 

1  =  muscles  front  of  calf. 

II  =  muscles  back  of  thigh. 

2  =  muscles  front  of  thigh. 
Ill  =  muscles  of  spine. 

3  =  muscles  of   abdominal 

wall. 
4,  5  =  muscles  of  front  of 

neck. 
Arrows  indicate  direction  of 

action  of  muscles. 


200  STUDIES   IN  PHYSIOLOGY 

to  stand  erect,  yet,  if  we  stop  to  think  of  it,  in  this  ap- 
parently simple  process  a  great  many  muscles  must  act 
together  at  the  same  instant.  That  this  cooperation  of  the 
muscles  is  due  to  the  control  exercised  by  nerve  tissue  is 
proved  by  the  fact  that  faintness  or  any  sudden  shock  to 
the  nervous  system,  destroys  for  the  time  being  the  power 
of  standing.  Not  only  must  the  muscles  of  a  small  child 
be  developed  before  it  can  support  itself  on  its  feet,  but  the 
brain  cells  and  nerves  also  must  be  educated.  The  ten- 
dons of  the  muscles,  we  have  found,  run  over  the  joints,  and 
the  muscles  are  arranged  in  pairs.  In  standing,  the  various 
joints  (ankle,  knee,  thigh,  trunk,  and  neck)  are  kept  rigid 
by  the  combined  pull  of  both  extensors  and  flexors.  Small 
wonder,  then,  that  it  takes  a  child  a  year  or  two  to  learn  to 
stand,  for  more  than  a  dozen  sets  of  muscles  must  be  taught 
to  work  harmoniously  (see  Fig.  93). 

Walking.  —  When  standing,  one  makes  the  muscles  of  one's 
limbs  contract  at  one  and  the  same  time.  Walking,  on  the 
other  hand,  involves  the  successive  action  of  the  various 
flexors  and  extensors.  If  we  are  standing  with  both  feet 
together,  and  put  the  right  foot  forward,  the  motion  is 
accomplished  by  the  flexor  muscles  in  front  of  the  hip  joint. 
We  then  touch  the  right  heel  to  the  ground,  and  later  the 
whole  sole  of  the  foot.  Meanwhile  the  body  has  fallen 
forward  so  its  weight  comes  to  rest  on  the  right  leg.  A 
forward  push  is  given  with  the  toes  of  the  left  foot  by  the 
contraction  of  the  big  extensor  muscle  at  the  back  of  the  calf 
of  the  leg.  Walking  may,  therefore,  be  described  as  a  series 
of  falls  in  a  forward  direction,  in  which  the  balance  is  re- 
stored by  thrusting  out  the  other,  foot.  Not  only  are  the  leg 
muscles  used  in  this  form  of  locomotion,  but  also  many  other 
muscles  are  brought  into  play.  Thus  it  is  easier  to  walk  if 
the  arms  are  allowed  to  swing.  The  whole  body  sways  more 
or  less  from  side  to  side  as  well  as  backward  and  forward, 
and  this  involves  motion  between  the  vertebrae. 

Running.  — •  When  one  is  walking,  one  foot  or  the  other  is 


A  STUDY  OF   THE   MUSCLES  201 

always  touching  the  ground.  In  running  there  are  instants 
of  time  when  neither  foot  touches  earth.  Kunning  differs 
from  walking,  too,  in  that  the  heel  does  not  touch  ground  in 
running ;  for  when  the  foot  is  thrust  forward,  one  lights  upon 
his  toes  alone,  and  then  the  toes  of  the  other  foot  give  the 
body  a  vigorous  push  forward. 

2.   INVOLUNTARY  MUSCLE 

Nerve  Control.  —  We  have  denned  involuntary  muscle  as 
tissue  that  contracts  and  relaxes  without  being  controlled 
by  the  will  power.  This  does  not  mean  that  the  nervous 
system  has  no  control  over  it,  for,  as  we  have  already  learned, 
its  action  is  directed  by  a  special  mechanism  in  the  trunk  of 
the  body  called  the  sympathetic  nerve  system. 


•7* 

FIG.  94.  — A  Plain  Muscle  Fiber. 

/  =  cell  body. 

n  =  nucleus. 

P  =  granular  substance  near  the  nucleus. 

Functions.  —  Involuntary  muscle  makes  up  most  of  the 
thickness  of  the  walls  of  the  heart,  of  the  alimentary  canal, 
and  of  the  blood  vessels.  It  is  an  experience  common  to  all 
of  us  that  processes,  like  the  winking  of  the  eyes,  breath- 
ing, and  walking,  are  carried  on  without  conscious  thought. 
We  can,  however,  close  the  eyelids  when  we  wish,  breathe 
rapidly,  slowly,  or  stop  breathing  for  a  time,  and  can  con- 
sciously direct  the  leg  movements  in  walking.  These 
activities  are,  therefore,  regarded  as  automatic,  and  the 
muscles  that  carry  on  these  movements  are  voluntary  muscles. 
Involuntary  muscles  carry  on  the  functions  that  are  beyond  the 
control  of  the  will. 

Structure  of  Involuntary  Muscle.  —  If  a  piece  of  stomach 
muscle  is  teased  apart  with  needles  and  then  examined  with 
a  compound  microscope,  this  tissue  is  found  to  consist  of 


202 


STUDIES  IN  PHYSIOLOGY 


small  sliver-shaped  cells,  each  having  a  nucleus.  Unlike  the 
voluntary  muscle  fibers  these  have  no  cross  stripes,  and  hence 
this  kind  of  tissue  is  often  called  un- 
striped  or  plain  muscle.  The  cells  are 
usually  joined  in  such  a  way  that  they 
form  thin  sheets.  They  are  supplied 
with  branches  of  blood  vessels  and  with 
nerve  fibers  from  the  sympathetic  nerve 
system. 

Heart  Muscle.  —  While  heart  muscle 
is  involuntary  so  far  as  its  action  is 
concerned,  in  its  structure  it  presents 
certain   peculiarities.      Like   other  in- 
voluntary muscles,  it  consists  of  sepa- 
rate cells,  each  with  a  distinct  nucleus. 
FIG.  95.— Two  Muscle   (It    is   impossible   to   distinguish    the 
Fibers  of  the  Heart.       outlines    of    cell    bodies    in    voluntary 

J  =  line  of  junction  be-  muscies.)      But,   on    the    other    hand, 

tween  two  cells.  ' 

n  =  nucleus.  heart  muscle  resembles  voluntary  mus- 

p  =  processes   which  cle  in  its  cross-striped  appearance.    The 
joined    another  1,1  i  ,-,  «     •  ,1 

fiber  muscles  that  make  up  the  wall  of  the 

heart  contract  more  rapidly  than  do 
other  involuntary  muscles,  but  less  rapidly  than  other 
cross-striped  tissue. 


3.   THE  HYGIENE  OF  MUSCLE 

Necessary  Conditions  for  Healthy  Muscles.  —  If  one  is  to 
have  'a  well-developed  and  healthy  muscular  system,  four 
conditions  must  be  fulfilled :  the  body  must  be  supplied  with 
nutritious  food  ;  there  must  be  a  generous  amount  of  fresh 
air ;  the  muscles  must  be  exercised  vigorously  ;  and  this  exer- 
cise must  be  followed  by  periods  of  rest.  We  will  now  consider 
in  turn  how  each  of  these  requirements  can  be  met. 

Food. — We  have  learned  that  75%  of  muscle  is  com- 
posed of  water,  and  that  proteid  is  the  most  important 


A   STUDY   OF  THE   MUSCLES  203 

solid  ingredient.  Mineral  matter  and  fats  are  also  present 
in  small  quantities,  even  in  the  leanest  of  muscle.  During 
the  period  of  growth  all  these  nutrients  should  be  sup- 
plied for  muscle  building,  but  proteid  is  absolutely  essen- 
tial. Grape  sugar  is  also  found  to  be  an  important  food 
during  muscular  contraction.  When  training  for  contests 
the  diet  of  athletes  is  carefully  regulated:  rare  meats, 
coarse  breads,  eggs,  vegetables,  and  fruits  are  supplied  in 
generous  quantities ;  pastry  and  fats  are  reduced  to  a  mini- 
mum. Tobacco '  and  alcohol  in  any  form,  however,  are 
absolutely  prohibited.  Such  a  diet  is  undoubtedly  far  more 
wholesome  to  develop  a  healthy  boy  or  girl,  man  or  woman, 
than  are  the  rich  gravies,  pastries,  and  condiments  which 
are  found  on  too  many  tables. 

Fresh  Air.  —  Healthy  muscle  is  absolutely  powerless,  how- 
ever, unless  in  addition  to  food,  it  receives  a  supply  of  oxy- 
gen; for  all  muscular  energy  is  produced  by  oxidation. 
Impure  air,  besides  being  deficient  in  oxygen,  contains  carbon 
dioxid  and  other  gases  that  are  exceedingly  harmful  to  the 
tissues  (see  p.  221).  Well-ventilated  sleeping  rooms  are 
most  essential  for  healthy  living,  for  during  the  night  the 
body  gets  rid  of  much  of  the  waste  carbon  dioxid  that  is 
formed  during  the  day. 

Exercise.  —  It  seems  like  a  contradiction  to  say  that  the 
only  way  to  get  more  and  better  muscle  is  to  destroy  what 
we  already  have.  Every  one  knows,  however,  that  if  the 
muscles  of  the  arm  or  the  leg  are  not  used  for  a  time,  they 
become  weak  and  flabby,  and  yet  every  time  a  muscle  is 
made  to  contract,  some  of  its  substance  is  oxidized.  New 
muscle  must  then  be  formed  by  the  process  of  assimilation 
to  take  its  place. 

A  certain  amount  of  vigorous  exercise  each  day  is  essen- 
tial if  one  is  to  keep  one's  body  in  the  best  physical  condi- 
tion. This  amount  of  course  varies  with  the  individual.  It 
should  never  be  carried  to  an  excess,  resulting  in  exhaustion, 
but  should  usually  be  at  least  the  equivalent  of  a  five-mile 


204  STUDIES  IN  PHYSIOLOGY 

walk  or  a  fifteen-mile  bicycle  ride.  Fortunate  is  the  boy 
who  can  spend  the  early  years  of  his  life  in  the  country, 
and  who  has  been  taught  to  do  a  certain  amount  of  manual 
work  each  day  out  of  doors.  Regularity  in  exercise  is  as 
important  as  regularity  in  eating.  One  cannot  exercise 
vigorously  one  day  and  expect  its  good  effects  to  last  for  a 
week.  We  should  not  call  upon  the  muscles  for  violent 
exertion  immediately  after  rising  and  before  breakfast,  nor 
should  we  exercise  until  at  least  a  half  hour  after  eating. 
The  physiological  reasons  for  these  directions  have  been 
already  given  in  our  study  of  the  circulatory  system  (p.  153). 

The  best  forms  of  exercise  are  those  that  call  into  play 
the  greatest  number  of  muscles.  For  this  reason  gymnasium 
training  is  better  than  many  kinds  of  outdoor  sports.  In 
the  gymnasium,  too,  special  forms  of  exercise  can  be  taken  to 
develop  any  muscles  found  to  be  weak.  On  the  other  hand, 
lawn  tennis,  golf,  rowing  and  football  have  the  additional 
advantage  of  being  played  in  the  open  air,  and  games  of  this 
sort  are  usually  more  exhilarating  than  are  set  forms  of 
exercise  with  apparatus.  To  secure  the  full  effect  of  any 
kind  of  exercise,  it  should  be  followed  by  a  moderately 
warm,  then  by  a  cold  shower,  or  sponge  bath,  and  by  a  good 
rubbing  of  the  body  with  a  coarse  towel. 

Muscles  are  not  the  only  tissues  developed  by  exercise. 
Every  muscular  contraction  is  directed  by  some  kind  of 
stimulus  from  the  nervous  system.  Before  the  muscles  of 
the  arm  or  leg  contract,  a  "  message "  must  come  to  them 
from  the  brain  or  spinal  cord ;  hence  nerve  tissue  is  likewise 
developed  by  exercise. 

Rest.  —  If  physical  exertion  is  carried  beyond  a  certain 
point,  exhaustion  results,  and  the  muscles  cannot  be  made  to 
contract  until  after  a  period  of  rest.  Since  all  muscular 
contraction  involves  metabolism  of  tissue,  periods  of  rest  must 
be  allowed  for  the  muscles  to  get  rid  of  their  wastes  and  to 
build  up  new  tissue  in  place  of  the  old.  The  feeling  of 
weariness  after  long-continued  exercise  is  probably  due  to 


A  STUDY   OF  THE   MUSCLES 


205 


the  presence  in  the  body  of  great  quantities  of  carbon  dioxid, 
water,  and  urea.  One  can  often  rest  to  good  advantage  by 
changing  from  one  form  of  activity  to  another,  but  from 
eight  to  nine  hours  of  sound  sleep  each  night  are  indispens- 
able for  the  health  of  a  growing  youth.  The  necessity  for 
sleep  will  be  further  discussed  in  the  study  of  the  nervous 
system. 


4.   A  COMPARATIVE  STUDY  OF  LOCOMOTION 

Amoeba.  —  We  have  already  studied  the  method  of  loco- 
motion of  amoeba  (see  p.  24),  and  we  have  seen  that  there 
are  certain  cells  in  the  human  body 
(white  blood  corpuscles)  that  show  a 
similar  amoeboid  movement.  In  all 
these  cells  the  whole  cell  body  may  be 
said  to  have  a  power  of  contraction 
something  like  that  seen  in  highly 
developed  muscle  tissue. 

Paramecium.  —  In  the  group  of  the 
Protozoa,  or  single  celled  animals, 
there  is  another  method  of  locomotion 
which  is  wonderfully  interesting.  If 
one  covers  some  hay  with  water  and 
allows  the  mixture  to  stand  for  a  few 
weeks,  on  examining  a  drop  of  this  so- 
called  hay  infusion  one  will  find  a 
multitude  of  microscopical  animals  Fia.96.— A  Paramecium. 
that  move  from  one  part  of  the  slide 
to  another  with  great  rapidity.  By 


c.  vac.  =  contractile  vac- 
uoles     (probably    for 
excretion) . 
adding  to  the  water  a  drop  of   gum    /.  Vac  =  food  vacuoles. 

arabic  or  other  sticky  solution,  their 
motions  can  be  retarded  so  that  one  is 
able  to  make  out  their  form  and  structure. 


gul.  =  gullet. 
mth.  =  mouth-opening. 


Each  par-a-me'- 
ci-um  (for  so  this  animal  is  called)  is  a  single  cell,  shaped 
something  like  the  sole  of  a  slipper.  Its  whole  outer  surface 


206  STUDIES   IN  PHYSIOLOGY 

is  covered  with  a  multitude  of  tiny  hairlike  projections  which 
are  called  ciVi-a,  and  these  wave  back  and  forth  like  little 
oars,  driving  the  animal  through  the  water.  In  paramecium, 
then,  the  outer  surface  only  is  adapted  by  the  cilia  for  loco- 
motion, whereas  all  the  cell  protoplasm  of  amoeba  may  be 
concerned  in  the  process. 

Earthworm.  —  If  one  watches  the  locomotion  of  an  earth- 
worm, one  sees  that  the  animal  first  pushes  forward  the  ante- 
rior end  and  then  draws  up  the  posterior  part  of  the  body. 
These  movements  are  accomplished  in  the  following  way. 
The  outer  wall  of  each  joint  or  segment  is  composed  of  (1) 
muscle  fibers  that  run  around  the  body  (circular  muscles), 
and  (2)  those  that  extend  from  the  anterior  to  the  posterior 
end  of  the  segment  (longitudinal  muscles).  When  the  circu- 
lar muscles  at  the  anterior  end  contract,  the  segments 
become  smaller  in  diameter,  but  longer.  If  now  the  longi- 
tudinal muscles  act,  the  joint  is  shortened,  and  in  this  way 
the  segments  behind  it  are  pulled  forward.  In  the  same 
way  the  circular  and  longitudinal  muscles  in  each  of  the 
hundred  joints,  more  or  less,  contract  successively,  and  thus 
a  wavelike  movement  passes  from  the  anterior  to  the  pos- 
terior end  of  the  body. 

The  forward  movement  of  the  worm  would  be  impossible, 
however,  if  there  were  not  some  means  of  anchoring  the 
segments  after  they  have  been  pushed  forward.  Let  one 
grasp  the  tail  end  of  a  worm  and  draw  the  rest  of  the  body 
across  the  finger  tip.  The  scratching  sensation  is  caused 
by  four  double  rows  of  tiny  bristles.  These  rows  extend 
the  whole  length  of  the  animal  on  its  ventral  surface.  To 
the  inner  end  of  each  bristle  are  attached  small  muscles  by 
which  it  can  be  pointed  either  forward  or  backward.  The 
bristles,  therefore,  not  only  make  the  ventral  surface  roughr 
but  also  serve  as  very  simple  appendages  to  assist  the 
longitudinal  and  circular  muscles  in  locomotion. 

Locomotion  in  Water.  —  Most  vertebrates  that  live  in  the 
water  are  provided  with  appendages  that  act  like  paddles. 


A  STUDY  OF  THE   MUSCLES  207 

Fishes  usually  have  two  pairs  of  fins  that  correspond  in  a 
way  to  the  arms  and  legs  of  man.  Their  principal  use 
is  to  steer  the  animal  through  the  water,  for  most  of  the 
force  for  the  forward  movement  is  supplied  by  the  muscles 
that  move  the  tail  from  side  to  side.  Such  rapid  movement 
is  possible  by  this  means  of  locomotion  that  the  salmon  is 
able  to  travel  twenty  miles  an  hour. 

Frogs  in  swimming  use  their  hind  legs  almost  wholly. 
All  the  joints  are  first  flexed,  thus  doubling  the  appendages 
near  the  body ;  they  are  then  quickly  straightened  by  the 
strong  extensor  muscles,  and  the  push  of  the  webbed  feet 
against  the  water  drives  the  body  forward  in  a  succession 
of  jerks.  Swimming  and  wading  birds  (ducks,  flamingoes) 
are  likewise  provided  with  webbed  feet.  Alligators  and 
crocodiles  swim  with  their  tails,  like  fishes. 

Locomotion  in  the  Air.  — Animals  that  fly  require  a  much 
more  highly  developed  muscular  system  than  do  those  that 
swim.  The  water  buoys  up  a  fish  and  furnishes  a  dense 
medium  for  the  fins  and  tail  to  push  against.  Air,  on  the 
other  hand,  is  eight  hundred  times  lighter  than  water.  We 
have  seen  that  the  skeleton  of  a  bird  is  made  light  by  the 
air  cavities  within  the  bones.  The  skeleton  of  a  crow 
weighs  when  dried  only  one  three-hundredth  of  a  pound. 

The  wings  of  a  bird  are  anterior  appendages  wonderfully 
adapted  for  locomotion  in  the  air,  since  great  extent  of  sur- 
face is  secured  by  the  expanse  of  feathers,  without  adding 
materially  to  the  weight  of  the  body.  The  powerful 
muscles  that  cause  the  quick  downward  movement  of  the 
wings  are  attached  to  the  breastbone.  This  has  the  form 
of  a  ship's  keel  in  flying  birds  and  serves  to  cut  the  air, 
while  the  tail  acts  like  a  rudder  to  steer  the  bird.  The 
hawk  is  able  to  fly  at  the  rate  of  one  hundred  and  fifty 
miles  an  hour. 

In  bats  the  long,  slender  finger  bones  are  covered  over 
and  connected  with  one  another  by  a  thin  skin,  and  thus 
there  is  formed  a  very  broad  but  light  kind  of  wing.  The 


208  STUDIES  IN  PHYSIOLOGY 

flight  of  bats  is  much  less  rapid,  however,  than  that  of 
birds. 

Locomotion  on  Land.  —  All  vertebrates  living  on  land,  with 
the  exception  of  snakes  and  a  few  rare  lizards  and  amphi- 
bia, are  provided  with  two  pairs  of  appendages.  The  legless 
snakes  move  forward  by  pushing  with  the  posterior  edge  of 
their  ventral  scales,  something  as  the  earthworm  uses  its 
bristles.  If  compelled  to  move  in  a  straight  line  their 
progress  is  slow;  but  by  curving  the  body  from  side  to 
side  (as  the  fish  moves  its  tail)  they  can  glide  along  with 
considerable  rapidity. 

Most  flying  birds  (robins,  sparrows)  use  their  posterior 
appendages  for  perching  on  a  support  or  for  hopping  and 
walking  along  the  ground.  Running  birds  (ostriches),  on 
the  other  hand,  and  most  domestic  fowls  (hens,  ducks, 
geese)  run  about  on  their  legs  much  like  the  human  being. 

The  hind  legs  of  the  four-footed  mammals  are  used 
mainly  for  pushing  the  body  forward,  the  front  legs  serving 
rather  as  a  means  of  support  for  the  head  end.  In  dray 
horses,  the  thigh  muscles  have  a  great  development,  while 
in  the  animals  that  spring  for  their  prey  (lions,  cats,  tigers) 
the  extensors  in  the  calf  of  the  leg  are  highly  developed. 


CHAPTER   XI 
A  STUDY  OF  RESPIRATION 

1.   NECESSITY  FOR  RESPIRATION 

Definitions.  —  Res-pi-ra'tion  (Latin  re  =  again  and  again 
+  spirare  =  to  breathe)  involves  two  distinct  processes : 
first,  that  of  taking  into  the  body  new  supplies  of  fresh  air, 
and  secondly,  that  of  removing  from  the  body  the  impure 
air  that  has  been  used.  To  the  first  process  is  given  the 
name  in-spi-ra'tion  (Latin  in  =  into  +  spirare  =  to  breathe); 
the  second  is  called  ex-pi-ra'tion  (Latin  ex  =  out  -f  spirare 
=  to  breathe). 

Necessity  for  Inspiration.  —  Every  contraction  of  the  mus- 
cles, every  activity  of  the  brain  or  of  gland  cells,  involves 
metabolism  in  these  various  tissues.  We  have  seen  that  the 
heart-  beats  more  rapidly  during  exercise,  and  this  means 
that  the  red  blood  corpuscles  are  being  hurried  into  mus- 
cular tissue  with  their  little  boat-loads  of  oxygen.  It  is  a 
familiar  fact,  too,  of  everyday  experience,  that  during  the 
activity  of  the  various  organs,  we  breathe  more  rapidly,  for 
as  oxygen  is  in  greater  demand,  more  must  be  furnished  to 
the  blood,  or  metabolism  in  the  tissues  will  be  retarded. 

Necessity  for  Expiration.  — •  Oxidation  necessarily  produces 
a  supply  of  the  compounds  we  have  classed  as  wastes.  Even 
when  we  are  sleeping,  the  heart,  the  kidneys,  many  of  the 
various  gland  cells,  and  some  of  the  nerve  cells  are  at  work, 
and  are  therefore  giving  to  the  blood  carbon  dioxid,  water, 
and  urea.  If  we  take  violent  exercise,  the  amount  of  these 
wastes  is  greatly  increased,  and  if  they  are  not  thrown  off 
from  the  body,  death  will  ensue,  for  they  will  finally  stop 
p  209 


210 


STUDIES  IN  PHYSIOLOGY 


the  processes  in  the  body  just  as  surely  as  does  an  accumu- 

lation  of  ashes  in  a  furnace. 
Wastes  given  off  by  Lungs. 
—  If  one  breathes  on  a  cold 
window  pane,  one  finds  that 
the  .glass  becomes  clouded 
with  vapor.  This  shows 
that  by  expiration  the  body 
gets  rid  of  some  of  its  waste 
water.  Carbon  dioxid  is  like- 
wise excreted  from  the  lungs, 
as  one  can  easily  demonstrate 
by  the  milky  appearance  of 
limewater  into  which  the 
breath  has  been  blown. 

2.   THE   ORGANS   OF  RESPI- 
RATION 


Course  taken  by  the  Air.  — 
Air  enters  the  body  through 
the  two  nostrils,  and  then 
passes  backward  into  the 
throat  cavity.  In  the  lower 
region  of  the  throat  is  the 
slitlike  glot'tis  opening, 
through  which,  when  the 
epiglottis  is  raised,  the  air 


FIG.  97. — Longitudinal  Section  of 
Head  and  Neck,  showing  Food  and 
Air  Passages. 

a  =  vertebral  column. 

6  =  esophagus. 

c  =  windpipe. 

d  =  larynx. 

e  =  epiglottis. 

/=  soft  palate  and  uvula. 


g  =  opening  of  left  Eustachian    enters  the  lar'ynx,  or  voice 

box.  The  latter,  commonly 
known  as  "  Adam's  apple," 
projects  somewhat  on  the 
ventral  side  of  the  neck,  and 
below  the  larynx  one  can 
feel  the  rings  of  cartilage 
Just  above  the  level  of  the  heart  the 


tube. 

h  —  opening  of  left  tear  duct. 
i  =  hyoid  bone. 
k  =  tongue. 
I  =  hard  palate. 
m,  n  =  base  of  skull. 
>,p,g  =  upper,    middle,    and    lower 
turbinate  bones. 


about  the  windpipe. 


A  STUDY   OF   RESPIRATION  211 

windpipe  divides  into  two  tubes,  the  right  and  left  bron'chus, 
each  of  which  supplies  air  to  one  lung  (see  Figs.  98  and  99). 


FIG.  98.  — The  Windpipe  and  its  Brandies  (dorsal  view). 

Ao  =  aorta.  M  =  opening  from  mouth. 

Br  =  bronchi.  PA  =  pulmonary  artery. 

D  =  diaphragm.  P  V  =  pulmonary  vein. 

Gl  =  glottis  opening.  RL  =  right  lung. 

H=  heart.  Tr  =  trachea  (windpipe). 

LL  =  left  lung.  V.C.L.  =  inferior  vena  cava. 

Within  the  lungs,  the  bronchi  branch  off  into  a  vast  num- 
ber of  very  small  pipes,  called  bron'chi-al  tubes.  The  finest 
divisions  of  these  pipes  open  into  extremely  thin-walled  air 
so.es  (Figs.  99  and  103). 

The  Nose  Cavity.  —  The  openings  into  the  nose  cavity  are 
guarded  by  a  forest  of  projecting  hairs,  through  which  the 
air  is  strained.  By  this  provision  a  considerable  amount 
of  dust  is  kept  from  entering  the  body.  The  nose  itself  is 
lined  by  mucous  membrane  which  covers  the  vomer,  the  up- 
per surface  of  the  hard  palate,  and  the  spongy  bones  which 
project  from  the  lateral  walls  of  the  nose  chambers.  Its  mu- 


212 


STUDIES  IN  PHYSIOLOGY 


cous  secretion  collects  most  of  the  dust  and  germs  that  have 
passed  the  hairs  in  the  nostrils.  Beneath  this  thin  lining 
are  countless  branches  of  blood  vessels,  which  act  like 
small  hot-water  pipes  to  warm  the  air  before  it  reaches  the 
throat  cavity. 


FIG.  99.  —The  Windpipe  and  the  Lungs. 

The  Throat  and  Larynx.  —  The  action  of  the  epiglottis  has 
been  already  described  in  connection  with  the  digestive  ap- 
paratus (see  p.  85).  Except  when  something  is  being  swal- 
lowed, the  glottis  is  always  open,  thus  allowing  a  free  passage 
for  the  air  from  the  throat,  through  the  larynx,  into  the  wind- 
pipe. All  the  varied  sounds  of  articulate  speech  which,  more 
than  anything  else,  distinguishes  man  from  other  animals, 
are  made  in  the  larynx.  The  structure  and  action  of  this 
wonderful  mechanism  will  be  discussed  in  a  later  chapter 
(see  chapter  XIV). 

The  Windpipe  and  its  Branches.  —  The  windpipe  and  its 
branches  are  kept  open  by  the  incomplete  rings  of  cartilage 


A   STUDY   OF   RESPIRATION 


213 


to  which  attention  has  already  been  called.  They  are  shaped 
something  like  a  letter  C,  the  open  ends  toward  the  dorsal 
surface  being  joined  by  the  con- 
nective tissue  that  surrounds  the 
windpipe  and  joins  the  rings  to 
one  another.  When  food  is  not 
being  swallowed,  the  windpipe 
presses  dorsally  and  closes  the 
esophagus.  As  food  passes  down- 
ward, however,  one  can  feel  the 
esophagus  push  the  air  tube  ven- 
trally. 

The  mucous  lining  of  the  wind- 
pipe and  its  branches  is  especially 
interesting.  The  cells  are  more 
or  less  cylindrical  or  club-shaped, 
and  their  inner  ends,  which  line 
the  air  passages,  are  covered  by 
minute  cilia  much  like  those  that 
cover  a  paramecium  (Figs.  96  and 
102).  The  cilia  alternately  wave 
upward  toward  the  throat  with  a 
quick  movement,  and  then  slowly 
recover  their  former  position.  In 
this  way  any  dust  particles  that 
have  passed  the  Carrier  of  hairs  at 
the  nostril  openings,  and  the  mucus 
secreted  by  the  membrane,  are 
moved  steadily  upward  until  they  reach  a  point  where  they 
can  be  coughed  out  into  the  mouth  cavity. 

The  Lungs.  —  One  can  get  a  good  idea  of  the  structure  of 
the  human  air-passages  and  lungs  by  securing  from  the 
butcher  the  "haslet"  of  a  sheep  or  a  calf.  This  consists 
of  the  larynx,  the  windpipe,  the  bronchi,  and  the  two  lungs, 
between  which  lies  the  heart  inclosed  in  the  pericardium. 
A  piece  of  the  diaphragm  is  often  attached  to  these  organs. 


FIG.  100.— Dorsal  View  of 
Larynx  and  Windpipe  cut 
longitudinally. 

a,  c,  t  =  cartilages  of  larynx. 
6,  6'  =  bronchi. 
e  =  epiglottis. 
h  =  hyoid  bone. 
tr  =  windpipe. 


214 


STUDIES  IN   PHYSIOLOGY 


Connective  tissue 
on  the  outside  of 
the  windpipe. 


Connective  tissue. 


^  Ciliated  cells  ol 
/  lining  of  wind- 
/  Pipe. 


FIG.  101.  —  Section  of  Wall  of  Windpipe,  magnified  about  50  times.    Photo- 
graphed through  the  microscope. 


The  lungs  are  composed  of  soft  pink  tissue,  easily  com- 
pressed by  the  hands.  If  air  is 
forced  through  a  tube  inserted 
in  the  glottis  opening,  the  lungs 
swell,  and  when  fully  distended 
they  occupy  a  space  several  times 
their  size  when  collapsed.  Just 
as  soon  as  ona  ceases  to  blow 
into  the  lungs,  one  sees  that  they 
begin  to  collapse,  and  soon  reach 
their  former  condition.  If  it 
were  possible  for  us  to  trace  out 
the  finest  branches  of  the  bron- 
chial  tubes,  we  should  find  that 

Flo.  102. -Ciliated  Cells  from  each  one  ended  in  a  branching 
the  Lining  of  the  Windpipe  of  a^r  sac  W^j1  extremely  thin  walls 
a  Rabbit,  highly  magnified.  «  ,  , .  , .  ,TT1_ 

of  elastic  tissue.   When  air  comes 

m,1  m,2  w3=mucous  cells  in  vari- 
ous stages  of  secreting  mucus,   into  these  air  chambers,  they  are 


A  STUDY   OF   RESPIRATION 


215 


FIG.  103.  — Two  Air  Sacs 
with  their  Branches. 


expanded;  but  as  expiration  begins, 
the  elastic  walls  help  to  force  back 
through  the  branches  of  the  windpipe 
the  air  that  has  been  taken  into  the 
lungs  (Fig.  103). 

Blood  Supply.  —  The  pulmonary  ar- 
tery, as  we  have  learned,  arising  from 
the  right  ventricle,  soon  divides  into 
two  branches,  one  for  the  right  and 
one  for  the  left  lung.  Within  the 
lung  tissue  each  blood  vessel  divides 
into  small  arteries  that  follow  the 
course  of  the  bronchial  tubes  to  the  « =  ending  of  a  bronchial 

air  sacs.     Here  the  arteries  communi-  tube. 

.,.  .„      .          ...     6  =  pouches  from  air  sacs, 

cate  with  a  maze  of  capillaries  which 

run  just  beneath  the  thin  lining  of  the  air  sacs.     It  is  here 

that  the  exchange  of 
material  takes  place  be- 
tween blood  and  the  in- 
haled air,  for  the  two 
are  separated  only  by 
the  extremely  thin  walls 
of  the  air  sacs  and  of 
the  capillaries.  From 
the  pulmonary  capillar- 
ies of  each  lung  the  blood 
is  carried  back  to  the  left 
auricle  by  two  pulmon- 
ary veins. 
FIG.  104.— Blood  Capillaries  (injected)  in  The  lungs,  like  all 

Walls  of  Air  Sacs.    White  Spaces  are  the    other      organs      of      the 

Cross  Sections  of  Air  Sacs.     Dark  Lines 

are  the  Capillaries,  magnified  about  30    body,     have      a      certain 

times.    Photographed  through  the  mi-    amOunt    of    work   to    do. 

Material  must  therefore 

be  provided  to  supply  the  waste  of  the  tissues.     This  is  fur- 
nished by  a  second  set.  of  arteries  (the  bronchial  arteries)  that 


216  STUDIES  IN  PHYSIOLOGY 

branch  off  from  the  thoracic  aorta  and  supply  minute  capil- 
laries to  the  walls  of  the  air  tubes,  air  sacs,  and  to  the  various 
blood  vessels;  for  the  larger  blood  vessels,  as  well  as  the 
heart,  must  receive  nutriment  from  the  outside,  since  they 
cannot  absorb  it  from  within.  Like  the  liver,  then,  the 
lungs  are  supplied  with  two  kinds  of  blood. 

The  Pleura.  —  The  outer  surface  of  each  lung  is  covered 
with  a  thin  layer  of  serous  membrane,  and  the  walls  of  the 
chest  cavity  are  lined  with  the  same  kind  of  tissue.  These 
two  layers  constitute  the  pleu'ra.  Both  surfaces  secrete  a 
serous  liquid  resembling  that  found  between  the  two  layers 
of  the  pericardium.  Hence  the  lungs  can  glide  over  the 
chest  wall  without  friction. 

The  Structure  of  the  Chest  Cavity In  the  upper  portion  of 

the  trunk  is  the  cone-shaped  chest  cavity,  which  is  more  or 
less  inclosed  by  the  sternum,  the  ribs,  the  collar  bones,  and  the 
spinal  column.  This  bony  framework  is  covered  by  muscle 
and  skin.  The  floor  of  the  chest  cavity  is  formed  by  the 
tough  sheet  of  muscle  and  connective  tissue  known  as  the 
di'aphragm  (Greek  diaphragma  =  partition  wall).  In  this 
way  there  is  formed  an  air-tight  compartment  which  is  com- 
pletely filled  by  the  heart,  the  blood  vessels,  the  esophagus, 
and  the  lungs. 

Enlargement  of  the  Chest  Cavity.  —  The  chest  cavity  is  not, 
like  most  boxes,  inclosed  by  rigid,  immovable  walls.  Let  one 
empty  one's  lungs  as  completely  as  possible,  and  then  place 
one  hand  on  each  side  of  the  body,  with  the  finger  tips  touch- 
ing on  the  ventral  surface  in  front.  On  taking  in  a  long 
breath,  one  feels  the  chest  cavity  enlarging  at  the  sides  and 
ventrally,  so  much  so  that,  if  the  palms  of  the  hands  are 
pressed  to  the  sides  of  the  body,  the  finger  tips  may  be 
separated  by  a  considerable  space.  At  the  same  time  the 
ventral  wall  of  the  abdominal  cavity  is  seen  to  be  pushed 
forward.  These  movements  prove  that  the  chest  cavity  can 
be  enlarged  in  three  directions,  namely,  from  side  to  side, 
from  dorsal  to  ventral  surface,  and  from  anterior  end  to 


A  STUDY  OF   RESPIRATION 


217 


posterior.  We  shall  now  consider  the  provisions  of  struc- 
ture that  make  this  possible. 

Movements  of  the  Ribs.  —  In  our  study  of  the  skeleton,  we 
learned  that  a  pair  of  ribs  is  joined  to  each  of  the  twelve 
dorsal  vertebrae,  and  that  ten 
of  these  pairs  are  attached 
to  the  breastbone  by  carti- 
lage. Most  of  the  ribs,  espe- 
cially the  lower  ones,  do  not 
run  on  a  level  from  the  spinal 
column  to  the  breastbone ; 
the  ventral  ends  are  consid- 
erably lower  than  are  the 
ends  connected  with  the 
backbone.  When  we  inspire, 
the  muscles  that  run  from 
the  anterior  part  of  the  trunk 
to  the  ribs  contract,  and  so 
the  ventral  ends  of  these 
bones  are  pulled  upward 
toward  a  horizontal  position. 

By  this  movement  the  breast-  The  dotted  lines  show  the  position  of 
,  .  ,,  ,  the  ribs  and  sternum  at  inspiration, 

bone  is  pushed  ventrally  and 

the  ribs  themselves  press  outward  at  the  sides  (see  Fig.  105). 
In  this  way  the  capacity  of  the  chest  cavity  is  increased 
from  side  to  side  and  from  dorsal  to  ventral  regions. 

Structure  and  Movements  of  the  Diaphragm.  —  When  the  dia- 
phragm is  relaxed,  it  forms  a  dome-shaped  partition  between 
the  heart  and  lungs  in  the  chest  cavity  and  the  stomach  and 
liver  in  the  cavity  of  the  abdomen  (see  Fig.  98,  D).  At  the 
apex  of  this  dome  is  a  tendon  formed  of  tough  connective 
tissue,  from  which  sheets  of  voluntary  muscle  run  outward 
and  posteriorly  on  all  sides.  The  muscle  fibers  are  attached 
to  the  lower  end  of  the  sternum,  to  several  of  the  lower 
ribs,  and  to  the  lumbar  vertebrae. 

When,  during  inspiration,  the  muscles  of  the  diaphragm 


FIG.  105. — Diagram  to  show  the 
Movements  of  the  Ribs  and  Ster- 
num in  Inspiration. 

c  =  cartilages  of  ribs. 
7-5,  r-6,  r?  =  5th,  6th,  and  7th  ribs. 

s  =  breastbone  or  sternum. 
.  v  =  vertebral  column. 


218 


STUDIES   IN  PHYSIOLOGY 


are  made  to  contract,  the  central  tendon  is  pulled  posteriorly 
upon  the  stomach,  liver,  and  other  abdominal  organs,  and 
these  in  turn  force  outward  the  wall  of  the  abdomen.  By 
the  action  just  described  the  size  of  the  chest  cavity  is 
increased  in  its  third  dimension, 
namely,  from  its  anterior  to  its  pos- 
terior end. 

How  the  Lungs  are  filled  with  Air.  — 
In  order  to  understand  the  way  the 
lungs  are  inflated,  we  may  study  to 
good  advantage  the  action  of  the  ap- 
paratus represented  in  Fig.  106.1 
Over  the  bottom  of  a  bell  jar  is 
stretched  a  piece  of  sheet  rubber,  in 
the  center  of  which  a  marble  is  tied. 
A  toy  balloon  or  the  lungs  of  a  cat 
are  fastened  to  the  lower  end  of  one 
of  the  glass  tubes  passing  through 
the  rubber  cork  in  the  top  of  the  bell 
jar.  To  the  upper  end  of  the  second 
glass  tube  is  attached  a  piece  of  rub- 
ber tubing  which  can  be  tightly  closed 
by  a  clamp.  The  bell 'jar  is  designed 
to  represent  the  walls  of  the  chest  cavity,  the  sheet  of  rubber 
answers  for  a  diaphragm,  while  the  glass  tube  and  rubber 
balloon  function  for  the  windpipe  and  one  lung. 

We  learned  in  the  first  chapter  that  the  air  exerts  a  pres- 
sure of  fifteen  pounds  on  every  square  inch  of  surface.  In 
the  apparatus  we  are  describing,  this  pressure  is  the  same 
on  the  inside  and  outside  of  the  bell  jar  and  of  the  balloon, 
and  above  and  below  the  sheet  rubber.  But  if  we  exhaust 
as  much  air  as  possible  from  the  bell  jar  through  the  rubber 
tube,  and  then  fasten  the  clamp,  we  reduce  the  pressure 
on  the  inside  of  the  bell  jar,  and  therefore  outside  the  bal- 
loon. Air  is  then  forced  by  atmospheric  pressure  down  the 
1  See  -;  Laboratory  Exercises,"  No.  38. 


FIG.  106.  —  Apparatus  to 
illustrate  the  Inflation 
of  the  Lungs. 


A   STUDY   OF   RESPIRATION  219 

tube  that  represents  the  windpipe,  and  in  this  way  the  rub- 
ber balloon  is  distended  until  it  nearly  tills  the  bell  jar.  At 
the  same  time,  the  outside  pressure  of  the  air  against  the 
sheet  rubber  forces  it  up  into  the  bell  jar,  and  its  like- 
ness to  the  form  of  the  diaphragm  becomes  even  more 
apparent. 

Let  us  now  seize  the  marble  and  pull  the  sheet  rubber 
downward.  The  cavity  within  the  bell  jar  becomes  larger, 
and  hence  the  inside  pressure  is  less.  More  air  rushes 
down  the  glass  windpipe  and  distends  still  further  the  rub- 
ber lung.  On  releasing  the  marble  we  find  that  the  dia- 
phragm moves  up  again  to  its  former  position,  and  that  some 
of  the  air  is  forced  out  of  the  lung. 

The  applications  of  the  experiment  to  the  action  of  the 
lungs  are  evident,  and  we  need  call  attention  only  to  certain 
points  in  which  the  experiment  fails  to  illustrate  the  process 
of  respiration.  In  the  first  place,  the  glass  bell  jar  allows 
no  movement  forward  and  backward,  and  from  side  to  side, 
as  do  the  walls  of  the  chest.  In  the  human  body,  there- 
fore, a  much  greater  expansion  of  the  lungs  is  possible  than 
in  this  apparatus.  Again,  nothing  corresponding  to  the  rub- 
ber tube  is  found  in  animals  with  lungs,  for  chest  cavities 
are  always  free  from  air.  And,  finally,  the  force  that  gives 
to  the  human  diaphragm  its  dome-shaped  form  is  exerted 
by  the  anterior  pressure  of  the  abdominal  organs,  not  by 
the  pressure  of  the  air,  as  is  the  case  in  our  experi- 
ment. 

Inspiration  and  Expiration.  —  During  inspiration,  then,  we 
enlarge  the  chest  cavity  by  pulling  upward  and  outward 
the  front  ends  of  the  ribs,  thus  pushing  ventrally  the  breast- 
bone, and  by  pulling  the  diaphragm  posteriorly.  A  greater 
space  is  thus  given  for  the  lungs,  and  the  air  rushes  in  from 
the  outside,  distending  the  elastic  lungs  and  keeping  them 
in  close  contact  with  the  walls  of  the  chest  cavity.  Inspira- 
tion requires  a  considerable  amount  of  muscular  effort,  for 
the  cartilages  attached  to  the  ribs  must  be  bent,  and  the 


220 


STUDIES  IN  PHYSIOLOGY 


abdominal  walls  must  be  stretched,  when  the  stomach  and 
liver  are  forced  downward. 

As  soon  as  the  muscles  that  cause  these  movements  begin 
to  relax,  the  ribs  sink  back  into  their  former  position,  the 
breastbone  is  pulled  back  into  place,  and  the  distended  wall 


FIG.  107.  —  Diagram  to  show  Changes  in  the  Breastbone,  Diaphragm,  and 
Abdominal  Wall  in  Respiration. 

A  =  inspiration.  D  =  diaphragm. 

B  =  expiration.  St  =  breastbone  or  sternum. 

Ab  =  abdominal  wall.  Tr  =  windpipe. 

The  shaded  part  is  to  indicate  the  stationary  air. 


of  the  abdomen  presses  the  organs  upward  against  the  dia- 
phragm, which,  therefore,  becomes  arched  again.  In  all 
these  ways  the  walls  of  the  chest  cavity  close  in  upon  the 
lungs,  and  thus  help  their  elastic  tissue  to  force  out  the  air 
in  expiration.  Ordinary  expiration  is  thus  accomplished 
without  muscular  effort. 


A  STUDY  OF  RESPIRATION  221 


3.   CHANGES  IN  AIR  AND  BLOOD  DUE  TO 

Temperature  of  Inspired  and  of  Expired  Air.  —  The  tem- 
perature of  a  room  in  which  we  are  living  and  working 
should  be  kept  as  near  to  68°  F.  as  possible.  Under  these 
conditions  the  air  that  enters  the  body  is  about  30°  cooler 
than  the  normal  temperature  within  the  body  (98  J°  F.). 
Let  one  breathe  upon  the  bulb  of  a  thermometer,  however, 
and  the  mercury  soon  registers  over  90°  F.  (some  heat  being 
lost  to  the  surrounding  air).  This  means  that  the  air  is 
heated  to  a  considerable  extent  within  the  body,  and  to  do 
this  the  body  must  give  up  a  corresponding  amount  of  heat. 

Composition  of  Inspired  and  of  Expired  Air.  —  The  air  that 
enters  the  lungs  consists  of  about  one  fifth  oxygen  and  four 
fifths  nitrogen.  The  latter  is  of  no  use  to  the  body,  and 
practically  all  of  it  is  sent  forth  in  expired  air.  About  one 
fourth  of  the  oxygen  of  fresh  inspired  air  is  taken  up  by 
the  blood  for  use  in  the  tissues  (one  and  four  fifths  pounds 
each  day). 

By  the  simple  experiments  suggested  on  p.  210,  we  dem- 
onstrated that  the  air  coming  out  of  the  lungs  contains 
considerable  quantities  of  water  and  carbon  dioxid.  In 
twenty-four  hours  the  body  rids  itself  by  this  means  of 
over  half  a  pound  (more  than  a  half  pint)  of  water,  and  of 
something  less  than  two  pounds  (422  quarts)  of  carbon 
dioxid  gas. 

At  the  same  time,  the  air  that  leaves  the  lungs  carries 
with  it  minute  quantities  of  ill-smelling,  poisonous  organic 
compounds.  It  is  the  latter  that  give  the  smell  of  closeness 
to  an  occupied  room  that  is  poorly  ventilated,  and  these 
make  expired  air  unwholesome  and  dangerous. 

Changes  in  the  Blood  while  passing  through  the  Lungs  -- 
Whatever  the  expired  air  has  gained  in  the  lungs  is,  of 
course,  lost  by  the  blood;  the  blood  also  takes  in  the 
ingredients  given  up  by  inspired  air.  The  change  of  color 

i  See  "Laboratory  Exercises,"  No.  40. 


222 


STUDIES   IN  PHYSIOLOGY 


from  purple  to  scarlet,  undergone  by  the  blood  in  the  pul- 
monary capillaries,  is  due,  as  we  proved  on  p.  121,  to  the 
absorption  of  oxygen.  The  various  exchanges  that  take 
place  between  blood  and  air  in  the  air  sacs  of  the  lungs  may 
be  stated  in  tabular  form  as  follows :  — 


OXYGEN 

NITROGEN 

WATER 

CARBON 
DIOXID 

ORGANIC 
COMPOUNDS 

Inspired  air  con- 

tains .... 

20+% 

80-% 

small  am't 

.0004% 

none 

Expired  air  con- 

tains .... 

15+% 

80-% 

consid.  " 

4  to  5  % 

small  am't 

Blood   .... 

gains  5  +% 

gains 

loses  con- 

loses 

loses  small 

none 

sid.  am't 

4  to  5  % 

amount 

4.   HYGIENE  OF  THE  RESPIRATORY  ORGANS 

Hygienic  Habits  of  Breathing.  —  We  have  called  attention 
(p.  211),  to  the  admirable  provisions  in  the  nose  for  filtering 
and  warming  the  air.  No  such  arrangements  are  provided 
in  the  mouth  cavity.  Hence,  if  one  breathes  through  the 
mouth,  one  is  likely  to  take  in  considerable  quantities  of  dust 
and  bacteria,  and  these,  in  the  long  run  are  likely  to  cause 
inflammation  or  other  form  of  disease.  Catarrh  is  an  acute 
inflammation  of  the  mucous  membranes  of  the  throat  and 
nose,  and  it  sometimes  becomes  so  bad  that  these  air  pas- 
sages are  more  or  less  closed.  If  one  has  this  trouble  with 
breathing,  one  should  at  once  consult  a  physician. 

Effect  of  Exercise  on  Respiration.  —  Not  only  does  the  heart 
beat  more  rapidly  during  exercise,  but  the  rate  of  breathing 
also  increases.  Oxygen  is  thus  supplied  in  larger  quanti- 
ties, and  more  wastes  are  eliminated.  .Deep  breathing  is  a 
prime  requisite  for  healthful  living,  since  in  this  way  the 
air  is  changed  throughout  the  lungs.  In  short,  quick 
breathing,  on  the  other  hand,  it  is  only  the  air  in  the  upper 
pulmonary  regions  which  is  thus  affected.  The  "second 
wind  "  that  the  runner  gets  after  a  short  time  is  due  to  the. 
expansion  of  all  portions  of  the  lung  tissue.  In  order  to 


A  STUDY  OF  RESPIRATION  223 

keep  the  chest  walls  flexible  and  capable  of  full  enlarge- 
ment, regular  exercise  should  be  persisted  in  throughout 
life. 

Effect  of  Tight  Clothing  upon  Respiration.  —  In  an  earlier 
part  of  this  chapter  we  learned  that  air  is  pumped  into  the 
lungs  when  the  ventral  ends  of  the  ribs  are  elevated  and  the 
diaphragm  is  pulled  downward  toward  the  horizontal  posi- 
tion. By  no  other  means  are  ths  respiratory  organs  filled 
with  air,  and  any  interference  with  the  action  of  either  ribs 
or  diaphragm  tends  to  decrease  the  supply  of  oxygen  and 
the  excretion  of  carbon  dioxid.  Tight  clothing  about  the 
chest  and  abdomen  not  only  results  in  permanent  distortion 
of  the  skeleton  (see  Fig.  79),  but  also  it  retards  the  move- 
ments by  which  the  chest  cavity  is  enlarged.  Shortness  of 
breath  and  inability  to  perform  any  great  amount  of  muscular 
exercise  are  some  of  the  ill  effects  that  are  experienced  from 
tight  lacing.  Diseased  conditions  of  the  organs,  too,  may  be 
brought  about  when  they  are  thus  compressed  and  forced 
out  of  position.  It  is  especially  important  that  loose  cloth- 
ing be  worn  in  the  gymnasium,  or  during  any  vigorous 
exercise,  in  order  that  the  muscles  used  in  motion  and  respir- 
ation may  be  free  to  work  unhampered. 

Diseases  of  the  Respiratory  Organs.  —  Colds,  we  have  found, 
are  inflammations  of  the  air  passages  or  of  other  regions  of 
the  body.  If  the  malady  is  confined  to  the  nose  cavity,  we 
call  it  a  head  cold ;  if  it  is  seated  in  the  pharynx,  a  sore 
throat  results.  A  cold  on  the  chest  is  an  inflammation  of 
the  windpipe  or  bronchi.  If  the  bronchial  tubes  are  affected, 
their  lining  membrane  becomes  swollen,  a  considerable 
amount  of  mucus  is  often  secreted,  and  the  air  passages  are 
more  or  less  closed ;  this  is  bron-chi'tis.  And  finally,  if  the 
inflammation  affects  the  air  sacs,  pneu-mo'ni-a  is  caused. 

Diph-the'ri-a  and  membranous  croup  are  germ  diseases  pro- 
duced by  colonies  of  bacteria  that  grow  in  the  throat.  In 
the  progress  of  these  diseases  certain  poisons  called  tox'ins 
are  formed  by  the  growing  bacteria,  poisons  which  are  ab- 


224  STUDIES   IN  PHYSIOLOGY 

sorbed  into  the  blood,  often  with,  fatal  results.  The  anti- 
toxin (Greek  anti  =  against  -{-  toxikon  =  poison)  treatment  for 
diphtheria,  however,  has  proved  to  be  marvelously  effective 
in  dealing  with  this  disease. 

In  cases  of  pleu'ri-sy  the  covering  of  the  lungs  and  the 
lining  of  the  chest  cavity  (the  pleura)  become  inflamed, 
the  two  surfaces  rub  against  each  other,  and  sharp  pain  is 
felt  in  breathing.  After  a  time  the  pleura  secretes  an 
abnormal  amount  of  fluid,  which  takes  up  space  that  should 
be  occupied  by  the  lungs. 

But  more  to  be  dreaded  than  all  the  diseases  we  have 
mentioned,  because  it  is  more  common,  is  tu-ber-cu-lo'sis  of 
the  lungs,  commonly  known  as  consumption.  It  is  said  that 
one  seventh  of  all  the  people  who  die  are  carried  off  by  its 
ravages.  Yet  this  is  a  preventable  disease.  It  is  always 
caused  by  the  growth  within  the  lungs  of  a  rod-shaped  bac- 
terium known  as  ba-cil'lus  tu-ber-cu-lo'sis.  A  man  may  inherit 
weak  lungs,  but  he  will  never  have  consumption  unless  he 
takes  into  his  body  some  of  these  germs.  Once  within  the 
body,  and  finding  the  favorable  conditions  furnished  by  a 
weak  system,  these  microscopic  organisms  gradually  but 
surely  destroy  the  lung  tissue  unless  the  disease  is  arrested. 
Consumptives,  in  coughing,  often  eject  masses  of  this  wasted 
tissue  which  are  swarming  with  living  bacteria.  If  the 
sputum  falls  upon  the  floor  or  the  street,  it  soon  dries,  and 
the  bacteria  become  a  part  of  the  dust  driven  about  by 
the  wind.  In  this  form  they  are  likely  to  be  inhaled  by  the 
passer-by,  reach  the  lungs,  and  so  transplant  the  seed  of 
the  disease.  The  sputum  of  a  consumptive  patient  should, 
therefore,  be  carefully  collected  in  paper  receptacles  which 
can  be  burned  with  their  contents.  From  the  facts  here 
presented,  one  sees  some  of  the  reasons  that  should  lead  the 
public  to  insist  on  a  rigid  enforcement  of  the  rules  of  the 
Board  of  Health  with  reference  to  spitting  in  public  places.1 

1  See  "  Dust  and  its  Dangers,"  by  Dr.  T.  Mitchell  Prudden.  G.  P. 
Putnam's  Sons. 


A   STUDY   OF  KESPIRATION  225 

Coughing,  Sneezing,  Choking.  —  In  coughing  an  extra  amount 
of  air  is  first  drawn  into  the  lungs  and  then  suddenly  expelled 
through  the  mouth.  We  cough  when  the  air  passages  are 
irritated  by  inflammation  or  by  some  foreign  substance, 
which  the  forced  expiration  often  dislodges  and  removes. 
Before  sneezing  there  is  a  deep  inspiration,  and  then  the 
volume  of  air  is  usually  driven  out  through  the  nose. 
Sneezing  is  caused  by  a  tickling  of  the  mucous  membrane 
of  the  nose ;  it  can  be  prevented  by  pressing  firmly  upon 
the  upper  lip  beneath  the  nose.  When  food  gets  past  the 
epiglottis  into  the  windpipe,  choking  results.  In  cases  of 
this  kind  the  head  should  be  held  forward  (or  downward 
in  case  of  a  child)  and  sharp  blows  struck  between  the 
shoulders. 

Suffocation.  — We  have  learned  that  the  body  must  be  sup- 
plied continually  with  oxygen  and  that  its  wastes  must  be 
constantly  removed.  If  this  process  is  interrupted  even  for 
five  minutes,  fatal  results  are  almost  sure  to  follow.  By 
suf-fo-ca'tion  is  meant  some  interference  with  the  process  of 
breathing.  Suffocation  may  be  due  to  inclosure  in  a  small 
space  with  a  limited  supply  of  oxygen,  to  the  inhaling  of 
illuminating  or  other  gas,  or  to  immersion  in  water  (drown- 
ing). In  any  case  the  patient  should  be  at  once  brought  out 
into  fresh  air.  If  water  has  entered  the  air  passages,  he 
should  be  turned  face  downward  and  raised  by  lifting  the 
weight  of  his  body  on  your  hands  clasped  under  his  abdomen. 
In  this  position  the  water  can  flow  out  of  his  lungs  more 
easily.  If  respiration  is  feeble,  cold  water  should  be  applied 
to  his  face,  and  his  chest  should  be  slapped  vigorously.  If 
all  these  methods  fail  to  restore  vitality  and  if  the  aid  of 
a  physician  cannot  be  immediately  secured,  artificial  respira- 
tion should  be  attempted  at  once.  This  is  accomplished  by 
laying  the  patient  on  his  back,  with  a  rolled  coat  or  other 
support  beneath  his  shoulders.  His  mouth  should  be  open 
and  his  tongue  drawn  out.  His  arms  should  then  be  grasped 
firmly  at  the  elbows  and  pulled  upward  and  parallel  to  each 


226  STUDIES  IN  PHYSIOLOGY 

other  until  they  come  to  lie  above  the  head.  In  this 
way  air  is  drawn  in  through  the  nose  and  mouth.  When 
the  elbows  are  carried  downward  and  pressed  upon  the  chest> 
the  air  is  forced  out  of  the  body.  These  two  movements 
should  be  alternated  regularly  every  few  seconds,  and  hope 
of  resuscitation  by  this  and  other  means  should  not  be  aban- 
doned until  several  hours  have  elapsed. 

Necessity  of  Ventilation.  — Every  act  of  respiration  removes 
about  five  parts  of  oxygen  from  every  one  hundred  parts  of 
the  air  taken  into  the  body,  and  adds  to  each  one  hundred 
parts  over  four  parts  of  carbon  dioxid,  together  with  the 
poisonous  organic  compounds  mentioned  on  page  221.  One 
might  breathe  in  this  air  a  second  time  and  still  be  able  to 
extract  oxygen  from  it.  The  presence  of  chemically  pure 
carbon  dioxid  in  air  even  in  considerable  quantity  is  not 
necessarily  dangerous ;  but  to  take  into  the  body  again  the 
organic  wastes  that  have  once  been  given  off,  is  most 
unhealthful.  The  first  effect  of  foul  air  is  a  feeling  of 
sleepiness  and  headache,  and  if  larger  quantities  are  in- 
spired, the  body  becomes  poisoned.  We  see,  then,  the  abso- 
lute necessity  of  having  the  air  in  a  living  room  changed 
frequently.  The  air  that  has  been  once  used  must  be  removed 
and  a  fresh  supply  must  be  furnished;  this  is  what  is  meant 
by  ven-ti-la'tion. 

Methods  of  Ventilation.  —  It  is  important  to  remember  that 
fresh  air  is  not  necessarily  cold  air,  and  that  draughts  of 
air  are  not  required,  indeed  that  they  are  undesirable.  The 
problem  of  ventilation  is  that  of  furnishing  a  sufficient 
quantity  of  wholesome  air  of  the  proper  temperature,  and 
of  removing  the  foul  air.  It  is  evident  that  this  is  rather 
difficult  to  accomplish  in  schoolrooms  or  in  public  halls. 
Air  will  not  of  itself  circulate  rapidly  enough,  and  so  it  has 
to  be  forced  into  these  rooms  by  large  blowers  or  revolving 
fans  in  the  basement.  Hot-air  pipes  or  fans  are  likewise 
often  employed  at  the  top  of  the  ventilating  flues  to  draw 
out  the  foul  air.  Since  warm  air  is  lighter  than  cool  air,  the 


A  STUDY  OF  RESPIRATION  227 

former  should  enter  a  room  near  the  ceiling.  As  it  cools  it 
gradually  settles  toward  the  floor,  and  the  openings  into  the 
ventilating  shafts  should  be  found  at  the  lower  part  of  the 
room.  If  the  system  works  properly,  there  will  be  a  con- 
tinuous supply  of  warm,  fresh  air,  and  at  the  same  time  the 
air  that  has  once  been  used  will  be  drawn  off  through  the 
flues. 

Unfortunately,  in  most  of  our  dwelling  houses  little  pro- 
vision has  been  made  by  the  builders  for  proper  ventilation. 
Hence,  if  the  rooms  are  heated  by  steam,  we  frequently 
breathe  over  and  over  some  of  the  air  that  has  been  already 
expired.  This  can  be  obviated,  however,  by  ventilating  in 
the  following  way.  A  piece  of  board  two  or  three  inches 
wide  should  be  fitted  across  the  lower  end  of  the  window 
opening.  When  the  lower  sash  is  pulled  down  upon  it,  a 
space  is  left  between  the  upper  and  lower  sashes,  through 
which  fresh  air  may  enter  the  room  without  causing  a  direct 
draught.  In  order  to  secure  a  proper  circulation  of  air  an 
opening  of  some  kind  should  be  provided  at  the  opposite 
side  of  the  room. 

Furnace  heat  is  much  more  satisfactory  than  steam  from 
the  point  of  view  of  ventilation,  for  in  this  way  a  continual 
supply  of  fresh  air  is  furnished.  An  open  fireplace  is  one 
of  the  best  means  of  removing  foul  air,  and  when  a  fire  is 
burning  a  strong  current  up  chimney  is  assured. 

Proper  Methods  of  Sweeping  and  Dusting.  —  It  is  impossible 
to  prevent  all  dirt  particles  and  bacteria  from  entering  the 
respiratory  organs,  especially  when  one  lives  in  a  city,  yet 
the  amount  of  irritation  and  the  chances  of  acquiring  disease 
can  by  proper  care  be  greatly  lessened.  The  number  of 
germs  of  various  kinds  that  may  be  found  in  a  church,  school- 
room, theater,  or  living  room  has  been  proved  by  a  long 
series  of  experiments  to  be  enormous,  for  with  the  ordinary 
methods  of  cleaning  these  rooms,  very  few  of  the  germs  are 
removed.  When  a  room  is  swept,  most  of  the  light  dust 
particles  and  bacteria  are  raised  from  the  floor  and  mingled 


228  STUDIES  IN  PHYSIOLOGY 

with  the  air.  After  a  short  time,  the  room  is  "dusted," 
often  with  a  feather  duster.  The  germs  which  may  have 
settled  on  the  horizontal  surfaces  are  again  whisked  off  into 
the  air.  Few,  if  any  of  them,  are  gathered  up  in  the  floor 
dirt,  and  so  the  room,  so  far  as  bacteria  are  concerned,  is 
just  as  dirty  as  before.  Experiments  have  demonstrated, 
too,  that  the  number  of  germs  in  a  room  is  not  materially 
affected  by  ventilating  currents,  unless  there  is  a  strong 
draught. 

All  this  germ  dirt  can  be  removed,  however,  by  the  appli- 
cation of  a  few  common-sense  principles.  In  a  room  which 
has  not  been  used  for  three  to  four  hours,  practically  all  of  the 
germs  and  fine  dust  particles  have  settled  out  of  the  air  upon 
the  horizontal  surfaces.  Hence,  it  is  clear  that  after  a  room 
has  been  swept  (and  in  public  halls  this  should  be  done  at 
night),  a  considerable  time  should  elapse  before  dusting  is 
begun.  For  dusting  a  damp  cloth  should  be  used;  in  this  way 
all  the  particles  of  dirt  are  collected  and  can  thus  be  removed 
from  the  room.  Were  these  methods  of  cleaning  adopted, 
the  air  we  breathe  in  the  rooms  which  we  occupy  would  be- 
come practically  germ  free,  and  there  would  be  a  surprising 
decrease  in  the  number  of  colds  and  other  diseases  to  which 
the  flesh  seems  to  be  heir.1 

Carpets  and  draperies  collect  and  hold  quantities  of  dust. 
They  should  therefore  be  removed  to  the  open  air  when 
being  cleaned,  otherwise  the  dust  will  simply  be  driven  from 
one  part  of  the  room  to  another.  It  is  much  more  hygienic 
to  have  hard-wood  floors  covered  with  rugs.  Dirty  streets, 
too,  are  a  constant  source  of  dust  infection.  Most  of  the 
irritation  from  this  source  would  be  avoided,  however,  if 
the  citizens  insisted  that  the  streets  be  kept  watered, 
especially  when  they  are  swept. 

1  See  "  Dust  and  its  Dangers,"  by  Dr.  T.  Mitchell  Prudden.  G.  P. 
Putnam's  Sons,  New  York. 


A  STUDY   OF  RESPIRATION  229 

5.   A  COMPARATIVE  STUDY  OF  EESPIBATION 

Respiration  in  Single-celled  Animals.  —  Amoeba,  parame- 
cium,  and  other  single-celled  animals  take  in  oxygen  all  over 
the  surface  of  the  body,  obtaining  their  supply  from  the  air 
that  is  held  in  suspension  by  the  water.  In  these  animals 
of  small  size  the  oxygen  can  easily  penetrate  to  all  portions 
of  the  protoplasm,  and  hence  no  circulatory  system  is  neces- 
sary for  its  distribution.  Carbon  dioxid  can  likewise  be  sent 
off  from  all  parts  of  the  cell  surface. 

Respiration  in  the  Earthworm.  —  Eespiration  in  the  earth- 
worm is  carried  on  through  the  skin.  Any  one  at  all  familiar 
with  the  habits  of  these  animals  knows  that  their  skin  must 
be  kept  moist,  otherwise  they  die.  The  capillary  blood  ves- 
sels pass  close  to  the  surface  in  order  to  supply  the  blood 
with  oxygen  and  to  excrete  the  wastes.  If  the  skin  becomes 
dry,  the  blood  loses  a  great  deal  of  water  by  evaporation, 
and  the  hardened  outer  surface  shuts  off  the  supply  of 
oxygen. 

Respiration  in  Fishes.  —  The  water  in  which  fishes  live  is 
composed  of  one  part  oxygen  and  two  parts  hydrogen  (H20). 
Animals,  however,  are  unable  to  obtain  free  oxygen  by 
separating  it  from  the  hydrogen,  and  the  oxygen  they  use 
is  supplied  by  the  air  dissolved  in  the  water.  At  the  sides 
of  the  mouth  cavity  of  a  fish  are  slitlike  openings.  The 
water  taken  in  by  the  mouth  is  forced  through  these  open- 
ings, over  the  four  or  five  pairs  of  comb-shaped  gills,  to  the 
outside  of  the  body.  The  single  ventricle  of  the  fish  heart 
forces  the  blood  out  to  the  gills,  where  the  arteries  connect 
with  a  great  number  of  capillaries  running  close  to  the  gill 
surface.  Here  the  blood  takes  up  a  supply  of  oxygen  and 
loses  many  of  its  waste  matters  (see  Fig.  60). 

Respiration  in  Air-breathing  Animals.  —  Toads  and  frogs, 
when  hatched  from  the  egg,  begin  their  life  as  tadpoles.  In 
this  state  they  are  really  fishes.  They  breathe  by  gills  ;  and 
the  blood  circulation  is  like  that  of  a  fish.  While  the  legs 


230  STUDIES  IN  PHYSIOLOGY 

are  developing  on  the  outside  of  the  body,  lungs  are  forming 
within,  and  by  the  time  the  tail  has  disappeared  and  the 
legs  have  become  full-grown,  the  animal  is  provided  with  a 
good  pair  of  lungs  ready  for  air  breathing.  These  lungs  are 
very  simple  affairs,  however.  The  whole  interior  is  a  hollow 
cavity  connected  with  a  short  windpipe,  through  which  the 
animal  swallows  air  taken  into  the  mouth  cavity  through 
the  nostrils.  In  the  thin  walls  which  inclose  the  lungs,  run 
the  pulmonary  blood  vessels.  The  skin  of  the  frog  is 
always  moist,  and  a  considerable  amount  of  respiration  is 
carried  on  through  this  outer  surface  also,  much  as  respira- 
tion is  carried  on  by  the  earthworm. 

All  reptiles,  birds,  and  mammals  breathe  throughout  life  by 
lungs,  and  little,  if  any,  respiration  is  carried  on  through  the 
more  or  less  thickened  skin.  Respiration  is  most  complete 
in  the  birds,  since  air  sacs,  connected  with  the  lungs,  are 
found  in  the  neck,  wings,  abdomen,  and  legs,  and  even  run 
out,  as  we  have  already  learned,  into  the  cavities  of  the 
bones.  Hence,  if  the  windpipe  were  closed  and  an  opening 
were  made  into  one  of  these  air  sacs,  respiration  could  still 
be  carried  on. 

Comparison  of  the  Organs  of  Respiration  Studied. — In  single- 
celled  animals  the  whole  body  may  be  said  to  function  in 
respiration,  since  each  bit  of  protoplasm  takes  from  the  sur- 
rounding water  the  oxygen  it  needs  and  gives  off  to  the 
water  its  carbon  dioxid. 

The  respiratory  region  in  worms  is  somewhat  more  lim- 
ited and  specialized.  The  whole  outer  skin  functions  as  a 
lung,  but  a  circulatory  system  is  rendered  necessary  by  the 
size  of  the  animal  in  order  to  carry  oxygen  to  the  internal 
organs  and  to  remove  the  wastes  from  them. 

In  all  vertebrates  specialization  is  carried  still  farther, 
well-developed  gills  or  lungs  being  provided  to  carry  on  the 
function  of  respiration.  In  most  of  the  vertebrate  groups, 
too,  there  is  a  special  pulmonary  blood  system  to  carry  the 
blood  to,  through,  and  from  the  lungs. 


A  STUDY  OF  KESPIRATION  231 

The  rapidity  of  respiration  depends  very  largely  upon  the 
degree  of  activity  of  the  animal.  Earthworms  and  toads, 
for  example,  are  rather  sluggish  in  their  movements,  and 
therefore  require  a  relatively  small  amount  of  oxygen.  In 
the  warm-blooded  birds  and  mammals,  on  the  other  hand, 
metabolism  goes  on  at  a  rapid  pace,  and  new  supplies  of 
oxygen  must  be  hurried  into  the  body  to  help  keep  up  this 
process. 


CHAPTER   XII 
A  STUDY  OF  THE   SKIN  AND  THE  KIDNEYS 

Characteristics  of  the  Skin.1  —  The  whole  outer  surface  of 
our  bodies  is  encased  in  a  flexible,  elastic  skin  of  varying 
thickness  and  texture.  In  regions  like  the  palm  of  the  hand 
and  the  sole  of  the  foot,  for  instance,  the  skin  is  thick  and 
tough ;  the  covering  of  the  lips,  on  the  other  hand,  is  ex- 
tremely thin.  Over  the  distal  bones  of  the  fingers  and  toes 
are  the  nails,  and  all  parts  of  the  body,  with  the  exception 
of  the  palms  of  the  hands  and  the  soles  of  the  feet,  are 
covered  with  hair.  Both  the  hair  and  the  nails  are  modified 
parts  of  the  skin. 

Uses  of  the  Skin.  —  The  most  obvious  use  of  the  skin  is 
the  protection  it  affords  for  the  muscles  and  other  organs 
that  lie  beneath.  In  the  second  place,  it  has  a  countless 
number  of  sense  organs  which  receive  messages  from  the 
outside  of  the  body.  These  are  hurried  in  along  nerve  fibers 
to  the  spinal  cord  and  brain  ;  and  in  this  way  we  get  impres- 
sions of  temperature,  of  pressure,  and  of  pain.  Again,  by 
means  of  the  perspiratory  action  of  the  skin,  the  body 
throws  off  a  great  deal  of  water  and  small  quantities  of 
other  waste  matters.  And,  finally,  as  a  result  of  the  evapo- 
ration of  this  water  from  its  outer  surface,  the  body  loses  its 
surplus  of  heat,  and  so  keeps  an  even  temperature  of  981°  F. 

As  we  might  infer  from  all  these  uses,  the  skin  is  a  com- 
plex organ  composed  of  several  tissues.  We  shall  now  study 
its  structure  and  see  how  it  is  adapted  to  perform  the  four 
functions  we  have  just  enumerated. 

1  See  "  Laboratory  Exercises,"  No.  42. 
232 


A  STUDY   OF   THE   SKIN  AND   THE   KIDNEYS       233 


1.  ANATOMY  AND  PHYSIOLOGY   OF   THE  SKIN 

Layers  of  the  Skin.  —  The  skin  everywhere  consists  of  two 
distinct  layers  :  an  outer,  called  the  ep-i-der'mis  (Greek  epi— 
upon + derma  =  skin),  and  an  inner,  the  der'mis.  When  one 
gets  a  blister  by  burning  the  skin,  most  of  the  epidermis  is 
lifted  up  by  an  excessive  amount  of  lymph  that  comes  out 
of  the  bl'ood  capillaries  and  lymph  vessels.  In  a  blister  one 
can  easily  distinguish  the  white  epidermis  from  the  pink 
layers  of  the  dermis  lying  beneath. 

Characteristics  of  the  Epidermis.  —  Let  one  wash  with  soap 
and  water  the  surface  of  any  portion  of  one's  body  and  then 
rub  it  vigorously.  One  will 
find  that  thin  layers  of  the 
outer  skin  are  easily  removed 
and  rolled  into  tiny  cylinders. 
If  a  needle  be  inserted  into 
the  skin  that  covers  a  blister, 
the  touch  of  the  needle  will 
be  felt,  but  no  pain  is  caused, 
nor  does  the  blood  flow.  By 
means  of  these  simple  experi- 
ments we  learn  the  following  facts  in  regard  to  the  epidermis : 
(1)  the  outermost  layers  are  being  constantly  worn  away,  and 
hence  we  infer  there  must  be  a  constant  growth  from  beneath 
to  supply  this  loss;  (2)  blood  vessels  are  lacking  in  the 
outer  skin ;  and  (3)  nerve  fibers  are  present  in  the  epidermis ; 
for  we  are  conscious  when  the  covering  of  a  blister  is  touched. 

When  we  examine  closely  the  skin  on  the  palm  of  the 
hand  and  the  tips  of  the  fingers,  we  see  that  the  surface  is 
covered  by  a  great  number  of  ridges  that  run  in  many  cases 
more  or  less  parallel  to  each  other  (see  Fig.  108).  The  pat- 
tern formed  by  this  succession  of  ridges  and  grooves  varies 
on  different  fingers.  On  a  given  finger,  however,  it  persists 
throughout  life,  and  use  is  sometimes  made  of  this  fact  in 
identifying  criminals  by  finger  prints. 


FIG.  108.  —Surface  of  Palm,  mag- 
nified, showing  Ridges  and  Pores 
from  Sweat  Glands. 


234 


STUDIES  IN  PHYSIOLOGY 


If  one  examines  the  surface  of  the  skin  with  a  good  hand 
lens,  one  can  detect  the  openings  of  the  sweat  tubes  dotting 
the  tops  of  the  ridges,  and  on  a  warm  day  the  tiny  drops  of 
perspiration  can  be  seen  oozing  from  these  pores  (Fig.  108). 

Structure  of  the  Epidermis.  —  In  a  section  through  the  skin 
one  can  easily  distinguish  the  dermis  from  the  epidermis. 
The  latter  is  composed  of  many  layers  of  cells  piled  on  each 


Horny  layer. 


Epidermis. 


Columnar  cells. 


Papillae  of  dermis 

containing  blood 

vessels. 


Dermis. 


Nervous  papilla 
of  dermis. 


FIG.  109.  — Vertical  Section  of  Skin,  highly  magnified. 

other.  On  the  outside  surface,  however,  it  is  impossible 
to  make  out  the  separate  cells,  for  this  horny  portion  of  the 
skin  (Fig.  109)  is  composed  of  thin  scales  united  by  a  cement 
substance.  We  shall  soon  see  that  these  dead  scales,  which 
are  easily  rubbed  from  the  surface,  were  once  living  cells. 

In  the  deepest  part  of  the  epidermis  is  a  single  layer  of 
columnar  cells  standing  on  end  (Fig.  109).  These  are  the 
most  active  cells  of  the  epidermis.  They  absorb  nourishment 
from  the  lymph  that  oozes  from  the  blood  vessels  running 
through  the  dermis,  they  grow,  produce  new  cells  by  division, 


A  STUDY  OF  THE   SKIN  AND  THE   KIDNEYS      235 

and  these  daughter  cells  gradually  approach  the  surface  of 
the  skin  as  the  outer  layers  are  worn  away.  During  this 
process  the  cells  become  dryer  and  thinner,  until  finally  all 
their  protoplasm  dies,  and  they  become  the  outer  horny 
scales  to  which  we  referred  above.  This  layer  is  of  special 
use  in  protecting  the  more  delicate  cells  beneath. 

In  the  layers  of  the  epidermis  are  certain  irregular  cells 
of  very  dark  color  known  as  pigment  spots.  They  abound 
in  the  skin  of  a  negro  and  give  to  this  race  its  dark  color. 
The  skin  of  a  brunette  contains  more  pigment  granules  than 
that  of  a  blonde.  Freckles  are  due  to  an  increase  in  the 
amount  of  this  pigment,  caused  oftentimes  by  the  action  of 
the  sun. 

Structure  of  the  Dermis.  —  If  a  thick  piece  of -skin  were  to 
be  soaked  for  a  time  in  a  weak  acid  or  alkaline  solution,  one 
could  easily  pull  off  the  epidermis  from  the  dermis.  It 
would  then  be  seen  that  the  surface  of  the  latter  is  thrown  up 
into  numerous  cone-shaped  elevations  called  pa-pil'lce  of  the 
dermis,  which  fit  into  corresponding  depressions  in  the  under 
layer  of  the  epidermis. 

These  small  papillae  are  of  two  sorts  (see  Fig.  109).  One 
kind  is  supplied  with  loops  of  blood  capillaries,  which  thus 
bring  the  blood  near  to  the  living  cells  of  the  epidermis.  In 
the  papillae  of  the  second  class  are  little  sense  organs  called 
tactile  corpuscles,  from  which  nerve  fibers  run  in  to  connect 
with  the  spinal  cord  and  the  brain.1  These  highly  sensitive 
papillae  are  especially  numerous  on  the  palm  of  the  hand  and 
the  tips  of  the  fingers.  Here  they  are  arranged  in  rows  ; 
the  epidermis  fills  in  the  spaces  between  the  little  mountain 
peaks  of  the  same  range,  and  thus  are  formed  on  the  outer 
skin  the  ridges  to  which  we  have  already  referred  (Fig.  108). 

The  dermis  is,  therefore,  well  supplied  with  nerves  and 
with  blood  vessels.  The  larger  portion  of  this  layer  of  the 
skin,  however,  is  composed  of  loosely  arranged  fibers  of  con- 

1  The  consideration  of  the  skin  as  a  sense  organ  will  be  taken  up 
more  fully  in  connection  with  the  nervous  system. 


236  STUDIES  IN  PHYSIOLOGY 

nective  and  elastic  tissue.  Beneath  the  dermis,  too,  there  is 
a  large  amount  of  these  tissues,  in  the  meshes  of  which  fat 
is  deposited  in  considerable  quantity.  This  fatty  layer 
serves,  as  already  stated  (p.  50),  to  retain  the  heat  of  the 
body,  and  it  is  also  used  for  fuel  when  needed  for  the  pro- 
duction of  energy.  The  wrinkles  of  old  age  are  due  to  the 
fact  that  this  fat  has  been  drawn  upon  to  such  an  extent 
that  the  skin  fits  loosely  over  the  underlying  tissues. 

Nails.  —  The  horny  layer  of  the  epidermis  becomes  espe- 
cially developed  in  the  nails  of  the  fingers  and  toes.  Except 
at  their  projecting  ends  these  nails 
lie  upon  and  are  closely  attached 
to  the  dermis,  and  their  edges  and 
bases  are  covered  over  by  a  roll  of 
the  epidermis  (Fig.  110).  The  nail 
itself,  like  all  epidermis,  is  not  sup- 

FIG.  no. -Section  of  Nail  plied  with  blood  vessels,  its  general 
and  Parts  beneath.  pink  color  being  due  to  the  rich 

1,  2,  4  =  horny  cuticle  or  epi-  supply  of  blood  in  the  papillae  of 
^  dermis.  the  dermis  beneath.  Near  the  base 

9  12  =  dermis.  '  °^  the  nail?  however,  these  papillae 

are  less  numerous  and  the  nail  it- 
self is  more  opaque ;  these  facts  explain  the  presence  of  the 
whiter  area  known  as  the  lu'nu-la  (Latin,  luna  =  moon  + 
ula  =  little). 

Nails  increase  both  in  thickness  and  in  length  by  a 
growth  from  the  living  cells  on  the  under  surface  of  the 
nails  and  at  their  base.  If  the  nail  is  accidentally  torn  off, 
a  new  one  is  produced,  provided  these  deeper  cells  are  not 
injured. 

Hair. — A  second  modification  of  the  epidermis  is  the 
hair.  To  help  understand  the  way  hairs  are  placed  in  the 
epidermis,  one  might  imagine  the  head  of  a  fine  pin  to  be 
pushed  diagonally  against  a  thin  sheet  of  rubber  in  such  a 
way  as  to  form  a  deep  pit  without  breaking  the  surface. 
The  sheet  of  rubber  would  then  represent  the  epidermis, 


A  STUDY  OF  THE  SKIN  AND  THE  KIDNEYS      237 

and  the  depression  would  answer  to  the  hair  fol'li-cle  or  pit, 
from  which  projects  in  a  diagonal  direction  the  shaft  of  the 
hair  (represented  by  the  pin).  The  root  of  the  hair  is  there- 
fore a  considerable  distance  from  the  surface  of  the  skin; 
indeed,  it  is  usually  deep  down  in  the  fatty  layer. 


Oblique  section.throngh 
Papilla  of  hair         a  Pacinian  corpuscle 

FIG.  111.  —  Vertical  Section  of  Scalp,  highly  magnified. 

At  the  base  of  every  hair  is  a  cup-shaped  depression  into 
which  projects  a  third  kind  of  papilla  of  the  dermis.  TJiis 
is  supplied  with  both  blood  vessels  and  nerves.  All  the 
growth  of  the  hair  takes  place  in  the  cells  just  above  this 
papilla,  that  is,  in  the  lower  cells  of  the  epidermis.  The 
projecting  shaft  is  wholly  formed  of  dead  horny  cells. 

Hairs  usually  pass  up  through  the  dermis  and  epidermis 
in  a  diagonal  direction.  From  the  base  of  the  hair  follicle, 
on  the  side  toward  which,  the  hair  slopes,  minute  bundles  of 


238  STUDIES  IN  PHYSIOLOGY 

involuntary  muscle  run  out  toward  the  outer  regions  of  the 
skin  (Fig.  111).  When  these  muscles  contract,  hairs  are 
made  to  assume  an  erect  position,  or  in  other  words  to 
"  stand  on  end."  In  the  skin  of  a  cat  the  muscles  attached 
to  the  base  of  the  hairs  are  specially  developed. 

Glands  of  the  Skin. — Two  kinds  of  glands  are  found  in  the 
skin,  namely,  the  oil  or  se-ba'ceous  (Latin,  sebum  =  grease) 
and  the  sweat  or  per-spi'ra-to-ry  glands.  The  former  are 
found  in  most  parts  of  the  skin,  being  most  numerous  in 
the  scalp  and  in  the  skin  of  the  face.  Like  hairs,  however, 
they  are  wanting  on  the  palms  of  the  hands  and  the  soles  of 
the  feet.  Sweat  glands,  on  the  other  hand,  are  most  numer- 
ous in  the  regions  just  named.  One  writer  estimates  that 
there  are  2800  sweat  pores  on  every  square  inch  of  the  sur- 
face of  the  palm,  and  that  the  total  number  of  these  glands 
in  one's  skin  is  about  2,500,000. 

Sebaceous  Glands. — In  form  these  glands  resemble  small 
irregular  sacs  (see  Fig.  111).  The  mouths  of  the  sacs 
open  most  frequently  into  the  cavity  of  a  hair  follicle. 
The  cells  in  the  interior  of  the  gland  are  formed  into  a  kind 
of  oily  secretion  which  keeps  the  hair  from  becoming  dry 
and  brittle.  This  liquid  also  spreads  more  or  less  over  the 
surface  of  the  skin  and  makes  it  oily  and  less  permeable 
to  water.  At  the  edges  of  the  eyelids  the  sebaceous 
glands  are  especially  large  and  their  secretion  prevents  the 
lids  from  sticking  together. 

Perspiratory  Glands. — We  have  already  called  attention 
to  the  pores  that  may  be  seen  on  the  surface  of  the  epider- 
mis of  the  hand.  From  one  of  these  openings  one  can  trace 
in  a  section  of  the  skin  a  more  or  less  spiral  duct  inward 
through  the  epidermis  and  the  dermis,  until  in  the  fatty 
layer  below  the  skin  the  little  tube  coils  itself  into  a  knot 
(see  Fig.  111).  In  this  inner  region  a  fine  capillary  network 
runs  about  the  cells  of  the  gland.  Here  the  blood  and  lymph 
Jose  a  considerable  amount  of  water,  together  with  a  small 
amount  of  urea  and  salts.  These  ingredients  make  up  the 


A  STUDY  OF  THE   SKIN  AND  THE   KIDNEYS      239 

perspiration.  This  passes  upward  through  the  twisted  duct 
and  oozes  out  through  the  pore  upon  the  surface.  Hence 
the  skin,  in  addition  to  its  protective  and  sensory  functions, 
is  also  an  important  excretory  organ. 

There  are  two  kinds  of  perspiration,  insensible  and  sen- 
sible. In  the  former  the  sweat  evaporates  as  rapidly  as  it 
reaches  the  surface,  and  we  are  not  conscious  of  perspiring. 
That  the  process  is  going  on,  even  when  we  feel  cool,  can  be 
demonstrated  by  placing  the  palm  of  the  hand  on  a  cool 
mirror.  By  far  the  larger  amount  passes  off  in  insensible 
form.  During  exercise  or  on  a  hot  day  the  perspiration 
stands  in  drops  on  the  surface  of  the  body ;  this  condition 
is  known  as  sensible  perspiration. 

Heat  Regulation  in  the  Body. — The  temperature  of  the 
healthy  human  body,  as  we  learned  on  p.  221,  is  981°  F. 
This  does  not  vary  to  any  appreciable  extent  in  winter  or 
summer,  no  matter  how  vigorously  one  may  exercise.  Yet 
during  exertion  metabolism  goes  on  much  more  rapidly,  and 
a  great  deal  of  heat  is  thereby  caused.  What  then  becomes 
of  this  extra  heat  ? 

In  fevers  the  temperature  sometimes  runs  ten  degrees 
higher  than  the  normal.  At  this  time  we  know  that  the 
skin  is  dry  and  parched,  for  the  body  is  unable  to  perspire. 
We  may  infer,  then,  that  in  health  we  keep  cool  by  perspir- 
ing, and  such  proves  to  be  the  case.  During  exercise  the 
heart  beats  with  greater  rapidity,  and  the  heated  blood  is 
driven  more  rapidly  through  the  skin  as  well  as  through 
other  organs  of  the  body.  When  it  comes  in  contact  with 
the  two  and  a  half  millions  of  sweat  glands  of  the  skin,  a 
great  deal  of  water  is  given  out,  and  this  soon  reaches  the 
surface  and  collects  in  drops.  In  evaporating  this  water 
the  body  loses  its  surplus  of  heat,  just  as  a  stove  loses 
heat  when  it  causes  a  pan  of  water  to  pass  off  into  the  air  in 
the  form  of  vapor.  By  this  automatic  process  our  bodies 
keep  at  an  even  temperature,  whatever  may  be  the  condition 
of  the  air  or  the  degree  of  metabolism  within  us. 


240  STUDIES  IN  PHYSIOLOGY 


2.   HYGIENE  OF  THE  SKIN 

Importance  of  Bathing.  —  The  sebaceous  and  perspiratory 
glands  are  constantly  pouring  their  secretions  in  greater 
or  less  quantity  upon  the  skin.  As  the  water  evaporates, 
the  oil  and  the  solid  ingredients  of  the  sweat  are  left  behind. 
Unless  these  are  removed,  they  tend  to  clog  the  openings 
of  the  ducts  from  the  glands  and  so  interfere  with  the  work 
of  the  skin.  A  considerable  amount  of  these  substances  is 
doubtless  worn  away,  together  with  the  scales  of  the  outer 
skin,  by  friction  against  the  clothing.  But  if  the  skin  is  to 
carry  on  its  functions  to  the  best  advantage,  frequent  baths 
must  be  taken. 

Kinds  of  Baths. — The  oily  secretions  and  much  of  the 
accumulated  dirt  on  exposed  surfaces  of  the  skin  can  be 
removed  only  by  the  use  of  warm  water  and  soap ;  hence 
these  should  be  employed  upon  the  face  and  hands  two  or 
three  times  a  day  and  at  least  once  or  twice  a  week  upon 
the  whole  body.  Warm  baths  should  be  employed,  how- 
ever, for  their  cleansing  effect  only,  since  they  are  usually 
followed  by  a  feeling  of  lassitude.  One  is  much  more  likely 
to  catch  cold,  too,  after  exposure  to  warm  water,  as  it  opens 
the  pores  of  the  skin,  causes  the  arteries  near  the  surface 
to  dilate,  and  thus  increases  the  amount  of  perspiration. 
Unless  the  warm  bath  is  taken  just  before  going  to  bed, 
it  should  be  followed  by  a  quick  application  of  cold 
water. 

Cold  baths,  on  the  other  hand,  if  taken  under  proper  con- 
ditions, have  an  exhilarating  effect.  The  best  time  for  such 
a  bath  is  immediately  on  rising  in  the  morning.  Until  one 
becomes  accustomed  to  the  cold  temperature,  the  water  may 
be  applied  with  a  sponge.  The  body  should  then  be  rubbed 
vigorously  with  a  coarse  towel.  In  our  study  of  the  circu- 
lation we  referred  to  the  effect  of  heat  and  cold  upon  the 
arteries.  After  their  first  quick  contraction  caused  by  the 
contact  of  the  cold  water  with  the  skin,  the  blood  vessels 


A   STUDY   OF   THE   SKIN  AND   THE   KIDNEYS       241 

enlarge,  and  one  feels  all  over  the  body  a  warm,  healthful 
glow.  Baths  should  never  be  taken  immediately  after  eat- 
ing, since  the  blood  is  thereby  drawn  away  from  the  organs 
of  digestion.  Nor  should  one  remain  in  cold  water  until 
one  feels  a  chill.  If  the  warm  reaction  does  not  take  place 
after  the  bath,  the  latter  is  not  beneficial,  but  injurious. 
Cold  baths  are  undoubtedly  one  of  the  best  means  of  pro- 
tecting the  body  against  colds.  Shower  baths,  however,  are 
better  than  a  cold  plunge,  for  they  stimulate  both  by  the 
cool  temperature  of  the  water  and  by  the  force  with  which 
it  strikes  the  skin. 

Care  of  the  Hair.  —  The  oil  glands  are  most  numerous  in 
the  scalp,  and  if  the  skin  is  in  a  healthy  condition,  the 
hair  is  supplied  with  just  the  proper  amount  of  oil.  If  this 
secretion  dries,  however,  and  becomes  mixed  with  the  loose 
outer  scales  of  the  epidermis,  dandruff  is  caused,  and  this 
should  be  removed  by  vigorous  brushing  and  shampooing. 
Not  only  is  the  scalp  cleaned  in  both  of  these  ways  (if 
clean  brushes  and  combs  are  used),  but  the  friction  stimu- 
lates the  circulation  of  the  blood  through  the  scalp,  and 
good  blood  is  a  better  hair  tonic  than  any  external  applica- 
tion of  the  "  tonsorial  artist."  If  the  oil  supply  is  insuf- 
ficient and  the  hair  becomes  dry,  vaseline  may  well  be  used. 
The  scalp  should  be  well  dried  after  a  bath,  for  moisture  at 
the  roots  of  the  hair  tends  to  cause  decomposition. 

Care  of  the  Nails.  —  One  of  the  surest  means  of  detecting 
slovenly  personal  habits  is  by  watching  the  care  an  indi- 
vidual takes  of  his  finger  nails.  An  accumulation  of  dirt 
beneath  the  nails  or  jagged  edges  caused  by  biting  the  nails 
almost  always  indicate  a  want  of  good  breeding.  The  finger 
nails  should  be  carefully  cleaned  with  soap,  water,  and  a 
nail  brush  or  with  a  nail  cleaner,  but  never  with  a  penknife 
or  scissors,  for  metal  scratches  the  surface  and  makes  a  place 
for  the  lodgment  of  dirt.  The  most  convenient  method  of 
cutting  the  nails  is  in  a  curved  direction,  and  this  gives  them 
the  best  appearance.  The  roll  of  epidermis  about  the  lunula 


242  STUDIES   IN  PHYSIOLOGY 

should  frequently  be  moistened  and  pushed  back ;  otherwise 
this  outer  skin  is  likely  to  become  torn  and  to  form  the  so- 
called  "  hangnails."  These  are  often  a  source  of  great  dis- 
comfort and  sometimes  of  danger,  for  they  furnish  a  possible 
opening  for  infection  by  bacteria. 

Treatment  of  Burns.  —  We  have  already  suggested  the 
treatment  for  cuts  .and  bruises  of  the  skin  in  connection  with 
the  blood  system  (see  p.  153).  Another  form  of  accident  that 
may  injure  the  skin  is  a  burn.  The  affected  part  should  be 
covered  with  a  paste  of  baking  soda,  which  tends  to  lessen 
the  pain  by  keeping  out  the  air  and  by  reducing  the  inflamma- 
tion. A  mixture  of  linseed  oil  and  limewater  (known  as 
carron  oil)  is  also  a  good  remedy  to  keep  on  hand  for  burns. 
If  the  clothing  of  a  person  catches  fire,  the  flames  should  be 
extinguished  by  wrapping  him  quickly  in  thick  clothing  or 
pieces  of  carpet. 

Clothing.  —  The  warmth  of  certain  kinds  of  cloth  depends 
upon  the  fact  that  they  keep  the  heat  of  the  body  from 
escaping ;  in  other  words,  they  are  poor  conductors  of  heat. 
Good  conductors,  on  the  other  hand,  allow  the  heat  to  pass 
off  rapidly.  This  difference  in  fabrics  is  largely  due  to  the 
way  they  are  woven.  Wool,  for  instance,  is  usually  made 
into  cloth  that  is  loose  in  texture,  and  thus  it  can  hold  a 
considerable  amount  of  air  in  its  meshes.  Now,  dry  air  is 
a  poor  conductor  of  heat.  Woolen  clothing  is  therefore 
generally  used  for  winter  wear.  Cotton  and  linen  are 
tightly  woven,  and  heat  radiation  through  these  materials 
is  rapid. 

The  color  of  clothing,  too,  is  of  considerable  importance. 
This  can  be  shown  by  experimenting  with  two  pieces  of  ice, 
both  exposed  to  summer  heat.  If  we  cover  one  piece  of 
ice  with  a  dark  shade  of  cloth,  and  the  other  piece  with  a 
yellow  or  white  shade  of  the  same  material,  we  shall  find 
that  the  ice  melts  more  rapidly  under  the  former.  This 
means  that  dark  colors  absorb  the  heat  rays  of  the  sun, 
while  the  light  shades  tend  to  reflect  the  heat.  For  this 


A  STUDY   OF  THE   SKIN  AND   THE   KIDNEYS      243 

reason  we  are  accustomed  to  wear  dark-colored  clothing  in 
winter  and  light  colors  in  hot  weather. 

Another  important  consideration  that  should  be  borne  in 
mind  in  deciding  upon  the  proper  clothing  for  the  different ' 
seasons  is  the  capacity  0!*  various  fabrics  for  absorbing 
moisture.  Wool  and  silk  take  up  a  great  quantity  of  moisture 
and  give  it  off  slowly  by  evaporation.  Hence  in  temperate 
and  especially  in  changeable  climates,  underwear  is  prefer- 
ably made  of  these  materials.  Cotton  and  linen,  on  the  other 
hand,  can  hold  but  a  small  amount  of  moisture  ;  they  allow 
rapid  evaporation,  and  thus  expose  the  wearer  to  the  danger 
of  a  chill.  Frequent  attacks  of  cold  and  of  summer  diarrhoea 
are  said  to  be  prevented  to  a  considerable  extent  by  wearing 
a  flannel  band  about  the  abdomen. 

Effect  of  Alcohol  on  Body  Temperature.  — ."  The  action  of 
alcohol  in  lowering  the  temperature,  even  in  moderate 
doses,  is  most  important.  By  dilating  the  cutaneous 
vessels,  it  thus  permits  of  the  radiating  of  much  heat 
from  the  blood.  When  the  action  is  pushed  too  far,  and 
especially  when  this  is  combined  with  the  action  of  great 
cold,  its  use  is  to  be  condemned."  LANDOIS  and  STIRLING, 
"  Text-book  of  Human  Physiology." 

"  A  party  of  engineers  were  surveying  in  the  Sierra 
Nevadas.  They  camped  at  a  great  height  above  the  sea 
level  where  the  air  was  very  cold,  and  they  were  chilled  and 
uncomfortable.  Some  of  them  drank  a  little  whisky,  and 
felt  less  uncomfortable ;  some  of  them  drank  a  lot  of  whisky, 
and  went  to  bed  feeling  very  jolly  and  comfortable  indeed. 
But  in  the  morning  the  men  who  had  not  taken  any  whisky 
got  up  in  a  good  condition ;  those  who  had  taken  a  little 
whisky  got  up  feeling  very  miserable;  the  men  who  had 
taken  a  lot  of  whisky  did  not  get  up  at  all:  they  were 
simply  frozen  to  death.  They  had  warmed  the  surface  of 
their  bodies  at  the  expense  of  their  internal  organs."  T. 
LATJDER  BRUNTON,  London,  "Lectures  on  the  Action  of 
Medicine." 


244  STUDIES  IN  PHYSIOLOGY 


3.   A  COMPARATIVE   STUDY  OF   THE   SKIN 

The  Skin  of  Invertebrates.  —  In  single-celled  animals  like 
amoeba  and  paramecium,  although  the  outer  part  of  the 
protoplasm  is  more  dense  than  the  rest,  this  layer  cannot 
properly  be  called  a  skin,  for  skin  is  an  organ  composed  of 
several  tissues.  The  skin  of  the  earthworm  is  an  important 
organ  that  serves  for  protection,  respiration,  excretion,  and 
sensation.  We  have  already  referred  to  the  skeleton  formed 
by  the  coral  and  to  the  hard  outer  shells  of  insects,  lobsters, 
and  clams.  In  reality  all  these  outside  skeletons  are  modi- 
fications of  the  skin  whereby  these  animals  secure  more 
efficient  protection  against  their  enemies.  The  other  func- 
tions carried  on  by  the  human  skin,  namely,  those  of  sensa- 
tion, excretion  of  waste  matters,  and  the  regulation  of  heat, 
cannot  be  performed  through  a  hard  shell.  Hence  for  these 
processes  specially  developed  organs  in  other  parts  of  the  body 
are  necessary  (see  p.  252). 

The  Skin  of  Amphibia.  —  In  our  comparative  study  of 
respiration  we  observed  that  the  skin  of  tadpoles  and  frogs 
is  always  soft  and  moist.  These  animals  probably  carry  on 
all  four  of  the  skin  functions  mentioned  on  p.  232,  together 
with  the  additional  function  of  respiration.  The  outer  cover- 
ing of  the  toad  is  dry  and  warty,  but  none  of  the  amphibia 
are  supplied  with  scales,  feathers,  or  hairs,  structures  that 
are  characteristic  of  the  other  groups  of  vertebrates.  At 
certain  times  of  the  year  the  outer  layers  of  epidermis  are 
shed  by  toads  and  frogs,  and  a  new  layer  is  then  formed  by 
the  living  cells.  In  the  human  being  the  outer  skin  is  con- 
tinually worn  off  in  minute  bits,  except  after  certain  dis- 
eases, like  the  measles  and  scarlet  fever,  when  considerable 
pieces  come  off  at  one  time. 

The  Skin  of  Fishes  and  Reptiles.  —  Fishes  and  reptiles,  in 
most  cases,  have  a  characteristic  outer  covering  composed  of 
scales.  Fish  scales  are  usually  hardened  portions  of  the  epi- 
dermis, projecting  back  ward,  and  overlapping  like  the  shingles 


A   STUDY  OF   THE   SKIN   AND   THE   KIDNEYS      245 

on  a  house.  A  protective  covering  is  thus  formed  which 
does  not  hinder  in  any  way  the  locomotion  of  the  animal. 

Among  the  reptiles  there  are  several  types  of  scales. 
Snakes  are  covered  with  a  horny  epidermis  that  is  shed 
usually  in  a  single  piece.  In  the  rattlesnake  a  curious  record 
is  kept  of  these  inoultings,  for  when  the  rest  of  the  skin  is 
dropped  off,  the  two  or  three  end  joints  are  merely  slipped 
backward  a  little.  Every  moult,  therefore,  adds  a  new  rattle 
to  the  chain,  but  since  this  casting  of  the  skin  occurs  at 
irregular  intervals,  the  string  of  rattles,  even  if  complete, 
does  not,  as  is  commonly  supposed,  indicate  the  age  of  the 
snake. 

Crocodiles  and  alligators  are  incased  in  a  covering  of 
bony  scales  which  are  more  or  less  firmly  attached  to  each 
other,  thus  rendering  locomotion  on  land  slow  and  clumsy. 
These  scales  are  composed  of  both  epidermis  and  dermis. 

One  of  the  most  perfect  means  of  protection  found  in  the 
animal  kingdom  is  the  shell  of  the  turtle.  This  is  a  box 
minus  the  ends,  into  which  the  animal  can  withdraw  its  head, 
legs,  and  tail.  In  order  to  understand  this  curious  structure, 
one  must  examine  the  upper  shell  from  within.  There  the 
vertebrae  forming  the  spinal  column  become  evident,  but  they 
are  immovably  attached  to  the  shell  above,  except  in  the 
region  of  the  neck  and  tail.  The  shell  itself  is  composed 
partly  of  the  modified  spinous  and  lateral  processes  of  the 
vertebrae,  partly  of  bony  plates  formed  in  the  dermis,  and 
both  of  these  layers  are  covered  over  by  the  horny  epidermis. 
This  last  layer  is  the  much-prized  tortoise  shell  used  in 
making  ornaments. 

The  Skin  of  Birds.  —  Feathers  are  the  characteristic  cover- 
ing of  birds,  and  they  are  the  most  wonderful  of  all  skin 
structures.  In  no  other  way  has  such  a  degree  of  lightness 
been  combined  with  such  extent  of  surface  and  with  such 
strength.  If  we  study  the  wing  or  tail  feather  of  a  chicken, 
we  find  it  to  be  constructed  as  follows.  The  hollow  quill  by 
which  the  feather  is  attached  to  the  skin  of  the  bird  is  con- 


246  STUDIES  IN  PHYSIOLOGY 

tinued  through  the  feather  to  its  tip  as  the  shaft.  The  vane 
or  flat  surface  on  either  side  of  the  shaft  is  composed  in  the 
first  place  of  barbs  that  branch  out  in  a  diagonal  direction. 
From  the  side  of  each  barb  toward  the  tip  of  the  feather  (that 
is,  distally)  run  off  a  row  of  little  barbules  that  are  supplied 
with  tiny  hooks.  Along  the  other  (proximal)  side  of  the 
barb  are  plain  barbules,  and  the  hooks  of  the  barbules  just 
below  catch  on  to  these  barbules  when  the  feather  is  smoothed 
or  "  preened.''  The  feathers  on  the  wing  overlap  in  such  a 
way  that  in  the  downward  stroke  the  surface  of  the  wing  is 


FIG.  112.  —  Portion  of  Feather,  magnified. 
sh  =  shaft.    6  =  barb.    61  =  barbule  with  hooks. 

continuous.  When  the  wing  is  lifted  for  a  second  stroke, 
the  feathers  separate  and  allow  the  air  to  pass  between  them 
with  little  resistance. 

Not  all  the  feathers  of  birds  are  as  complicated  as  the 
quill  feathers  just  described.  Ostrich  plumes  have  no  hooks 
on  the  barbules,  and  hence  the  latter  do  not  cling  together. 
Egret  plumes  consist  of  shaft  and  barbs  only ;  all  barbules 
are  wanting.  And  finally,  about  the  beaks  of  some  birds  are 
simple  hairlike  structures,  corresponding  to  the  feather 
shaft.  Whatever  its  structure  may  be,  however,  a  feather, 
like  a  hair  or  a  nail,  is  always  a  modification  of  the  outer 
layers  of  the  skin. 

The  Skin  of  Mammals.  —  As  scales  are  the  distinguishing 
outer  covering  of  fishes  and  reptiles,  and  as  birds  are  char- 


A  STUDY  OF  THE   SKIN  AND   THE   KIDNEYS       247 

acterized  by  the  possession  of  feathers,  so  the  highest  group 
of  animals,  the  mammals,  are  distinguished  by  the  presence 
of  hair.  This  varies  in  amount  from  the  scattered  bristles 
on  the  body  of  a  whale,  and  from  the  numerous  thickened 
quills  that  protect  the  porcupine,  to  the  dense  hairy  cover- 
ing of  the  bear  or  the  sheep.  In  structure,  however,  all 
these  forms  of  hair  agree  more  or  less  closely  with  that 
already  described  for  human  hair. 

Many  animals  of  this  group  are  supplied  with  claws  that 
enable  them  to  seize  and  tear  their  prey.  Claws  differ  from 
human  finger  and  toe  nails  only  in  the  fact  that  the  former 
grow  on  all  sides  of  the  end  joint  of  the  animal's  append- 
ages. The  bone,  therefore,  forms  the  core  of  the  claw,  and 
it  is  inclosed  by  the  layer  of  horn.  Hoofs  of  horses,  cows, 
and  of  deer  are  formed,  like  claws,  by  a  horny  layer  that 
incloses  the  end  bone  of  the  various  digits  (see  Fig.  84). 
This  hoof  is  constantly  growing,  and  if  it  is  not  worn  away 
by  use,  it  has  to  be  pared  off,  as  is  the  case  when  the  horse 
is  shod. 

The  horns-  of  animals  are  of  two  kinds :  namely,  either 
hollow  or  solid.  The  horns  of  an  ox  are  formed  by  a  conical 
projection  of  the  frontal  bone,  which  is  covered  over  by 
dermis,  and  this  in  turn  is  incased  in  a  hard  layer  of  horny 
epidermis.  Hence,  on  removing  the  horny  part,  we  find 
that  it  is  hollow.  Successive  layers  are  formed  one  within 
another,  and  this  kind  of  horn  lasts  throughout  the  life  of 
the  animal.  Deer,  on  the  other  hand,  grow  new  horns  or 
antlers  each  year.  In  the  early  months  two  projections  grow 
out  from  the  frontal  bone  and  branch  with  great  rapidity. 
At  first  they  are  richly  supplied  with  blood  vessels  and  are 
covered  with  a  soft  layer  of  epidermis  that  looks  and  feels 
like  velvet.  Later  in  the  year  this  disappears,  the  antlers 
harden,  a  line  of  separation  is  formed  between  them  and  the 
skull,  and  they  finally  drop  off.  The  next  year  the  process 
is  repeated.  Horns  tvhich  are  hollow  are  therefore  perma* 
nent;  solid  antlers  are  deciduous. 


248  STUDIES  IN  PHYSIOLOGY 

4.   A  STUDY  OF  THE  SHEEP  KIDNEY* 

General  Appearance  of  the  Kidney.  —  One  can  secure  of  any 
butcher  the  kidney  of  a  sheep.  It  is  inclosed  in  a  mass 
of  fat.  On  pulling  this  away,  one  finds  a  thin  membrane 
of  connective  tissue  which  closely  envelops  the  kidney. 
When  this  covering  is  opened,  there  appears  a  dark  red 
organ,  more  or  less  elliptical  in  outline.  It  is  somewhat 
flattened,  too,  and  is  hollowed  in  on  one  edge,  —  in  fact,  it 
has  almost  the  exact  shape  of  a  bean  seed.  From  the  region 
of  the  hollow  or  hi'lum  of  the  kidney  passes  out  a  tube 
called  the  u-re'ter  (compare  with  Fig.  113).  Large  blood 
vessels  also  enter  and  leave  the  kidney  in  this  region. 

Longitudinal  Section  of  the  Kidney.  —  If  one  divides  this 
organ  in  halves  by  cutting  through  from  its  convex  edge  to 
the  hilum,  one  can  make  out  pretty  clearly  the  internal 
structure.  At  the  hilum  the  ureter  expands  into  a  consider- 
able cavity  called  the  pel'vis  of  the  kidney.  Around  this 
cavity  the  kidney  is  seen  to  be  divided  into  two  distinct  re- 
gions. The  outer  or  cor'ti-cal  (Latin  cortex  =  bark)  has  a 
dark  brownish  red  color  and  is  granular  in  appearance. 
The  inner  or  med'ul-la-ry  layer  is  made  up  of  cone-shaped 
masses,  and  the  apex  of  each  of  these  pyramids  projects  into 
the  pelvis  of  the  kidney.  The  general  appearance  of  the 
medullary  layer  is  red  and  glistening.  Fine  lines  run 
through  the  pyramids  from  base  to  apex. 

5.   ANATOMY  AND  PHYSIOLOGY  OF  THE  HUMAN  KIDNEY 

Position  and  Appearance.  —  In  shape  and  general  appear- 
ance human  kidneys  resemble  closely  these  organs  of  a 
sheep.  The  two  kidneys  are  attached  to  the  dorsal  part  of 
the  cavity  of  the  abdomen  in  the  region  of  the  loins,  and 
the  ureters  come  off  from  the  median  border  of  each.  In  the 
longitudinal  section  the  pyramids  of  the  medullary  layer 
are  seen  much  more  distinctly,  however,  than  in  the  sheep 

iSee  "Laboratory  Exercises,"  No.  44. 


A  STUDY  OF  THE   SKIN  AND  THE  KIDNEYS      249 


M 


RV 


kidney  described  above,  and  the  apex  of  each  pyramid 
projects  like  a  papilla  into  the  pelvis  or  enlargement  of  the 
ureter  (Fig.  113). 

Microscopical  Structure. — The  kidney  is  composed  of  an 
enormous  number  of  complicated  tubules  that  begin  in 
the  cortical  region,  pass 
through  the  medullary 
layer  (giving  the  appear- 
ance of  fine  lines  through 
the  pyramids  referred  to  at 
above),  and  finally  open 
on  the  summits  of  the 
pyramids  into  the  cavity 
of  the  organ.  At  the 
beginning  of  each  tubule 
is  a  tiny  spherical  swell- 
ing richly  supplied  with 
a  network  of  blood  vessels 
(Fig.  114).  Here  it  is 
probable  that  water  oozes 
out  of  the  blood  and  passes 
thence  through  the  tortu- 
ous course  of  the  tubule. 
The  latter  also  is  sur- 
rounded with  blood  capil- 
laries. Urea,  salts,  and 
other  waste  matters  are 
without  doubt  taken  out  of  the  blood  and  lymph  by  the  cells 
in  this  region  of  the  tube,  and  the  urine  thus  formed  passes 
through  the  winding  course  of  the  ducts  until  it  finally  oozes 
out  into  the  cavity  (pelvis)  inclosed  by  the  medullary  layer. 

Course  taken  by  the  Urine.  —  The  urine  is  therefore  secreted, 
to  a  large  extent  at  least,  in  the  cortex  of  the  kidney,  and 
thence  passes  through  the  pyramids  of  the  medullary  layer 
into  the  pelvis  of  the  organ.  From  this  cavity  in  each  kid- 
ney the  ureter  conducts  the  liquid  to  a  storage  sac  called  the 


FIG.  113.  —  Section  of  Human  Kidney. 

Ct  =  cortex. 

M  =  medulla. 

P  =  pelvis  of  kidney. 
Py  =  pyramids  in  medulla. 
RA  =  renal  artery  to  kidney. 
RV=  renal  vein  to  kidney. 

U=  ureter. 


250 


STUDIES  IN  PHYSIOLOGY 


u'ri-na-ry  bladder,  whence  it  is  discharged  from  the  body 
through  a  tube  called  the  u-re'thra. 

Importance  of  the  Kidneys.  —  The  kidneys  are  organs  of 
first  importance  in  ridding  the  blood  of  its  wastes.     If  they 
stop  work  altogether,  death  occurs  in  twenty-four  to  forty- 
eight  hours.  Fortunately 
3  M 


vf  at 


the  skin  can  help  to  a 
certain  extent  by  excret- 
ing an  abnormal  amount 
of  urea  and  salts.  Under 
ordinary  conditions  about 
three  pints  of  urine 
should  be  given  off  by 
the  kidneys  of  an  adult 
in  twenty-four  hours. 
This  amount  is  lessened 
if  perspiration  is  exten- 
sive. 

Blood  Supply  of  the 
Kidneys.  —  As  we  might 
expect  from  the  impor- 
tance of  their  function, 
these  organs  have  a  gen- 
erous supply  of  blood. 
A  large  branch  from  the 
abdominal  aorta  (re'nal 
artery)  enters  the  hilum 
of  each  kidney,  divides 

into  smaller  branches,  and  these  finally  reach  the  parts  of 
the  tubule  where  the  wastes  are  removed.  The  veins  that 
collect  the  blood  from  the  two  kidneys  (renal  veins)  empty 
into  the  inferior  vena  cava.  The  blood  in  these  two  veins 
(as  already  stated  on  p.  148)  is  probably  the  purest  in  the 
body;  it  comes  to  the  kidneys  almost  immediately  after 
giving  up  its  carbon  dioxid  in  the  lungs ;  and  before  leaving 
these  excretory  organs  it  loses  its  waste  urea,  salts,  and  water. 


FIG.  114.— Diagram  of  the  Circulation  in 
the  Kidney. 

ai  =  small  artery  giving  off  a  branch. 
6  =  parts  of  cortex  supplied  with  spher- 
ical swellings  (glomeruli). 
gl  =  spherical  swellings  (glomeruli)  from 

which  arises  a  twisted  tubule. 
va  =  branch  of  artery  to  spherical  swell- 
ing. 

ve  =  vein  from  spherical  swelling. 
v  =  veins  from  tubules. 


A  STUDY  OF  THE  SKIN  AND  THE   KIDNEYS      251 

6.   A  COMPARISON  OF  EXCRETORY  ORGANS 

Before  making  any  study  of  the  kidneys  in  various  groups 
of  animals,  it  will  be  well  to  compare  the  different  kinds  of 
excretory  organs  in  man*  We  must  first,  however,  distin- 
guish two  terms,  namely  — 

Secretion  and  Excretion.  —  Glands  and  their  functions  have 
been  referred  to  frequently  in  the  preceding  chapters.  We 
have  defined  a  gland  (p.  75)  as  an  organ  that  secretes  any 
kind  of  a  liquid.  Now,  the  liquids  made  by  glands  are  of 
two  kinds.  Some,  like  the  saliva,  gastric  and  pancreatic 
juices,  are  made  from  materials  furnished  by  the  blood,  and 
are  of  great  service  in  the  economy  of  the  body.  Such 
fluids  are  called  secretions.  Perspiration  and  urine,  on  the 
other  hand,  are  composed  of  highly  injurious  wastes.  They 
are  secreted  by  the  glands  of  the  skin  and  by  the  kidneys, 
it  is  true ;  but  since  these  liquids  are  of  no  use  to  the  body, 
and  are  at  once  thrown  off,  they  are  called  excretions. 

The  Kidneys  and  the  Skin.  —  Attention  has  been  called 
to  the  fact  that  the  work  of  the  kidneys  may  at  times  be 
performed  to  a  certain  extent  by  the  skin.  In  structure, 
likewise,  the  two  organs  are  somewhat  similar,  if  we  com- 
pare one  of  the  kidney  tubules  with  one  of  the  sweat 
glands.  Each  consists  (1)  of  a  region  richly  supplied  with 
blood  vessels  where  secretion  is  carried  on,  and  (2)  of  a 
tortuous  duct  that  carries  off  this  secretion.  On  the  other 
hand,  in  the  skin  the  glands  are  completely  separated  from 
each  other,  while  the  tubules  are  closely  massed  together  in 
the  kidneys.  The  most  striking  difference  is  seen,  however, 
when  we  compare  the  two  excretions.  The  principal  use  of 
the  urine  is  to  carry  off  the  poisonous  urea ;  the  perspiration 
serves  primarily  to  regulate  the  temperature  of  the  body. 

The  Lungs  as  Excretory  Organs.  —  If  respiration  ceases, 
death  ensues  in  five  to  ten  minutes,  and  this  is  largely  due 
to  the  fact  that  the  wastes  of  the  body  are  not  being  prop- 
erly removed.  The  lungs  are  therefore  the  most  important 


252  STUDIES   IN  PHYSIOLOGY 

of  the  excretory  organs.  Almost  all  the  carbon  dioxid 
formed  in  oxidation  is  given  off  from  the  lungs,  very  little 
being  excreted  by  the  kidneys  and  skin.  Water  is  given 
off  by  all  three  organs ;  urea  from  two  (kidneys  and  skin). 

The  Liver  as  an  Excretory  Organ.  —  We  learned,  on  p.  100, 
that  the  bile  contains  the  wastes  produced  by  the  destruc- 
tion of  red  corpuscles.  The  liver,  then,  besides  its.  func- 
tions of  storing  sugar  and  of  secreting  a  digestive  juice, 
must  be  regarded  as  an  organ  of  excretion. 

The  Kidneys  of  Vertebrates.  —  Hitherto  it  has  been  our 
plan  to  begin  the  comparative  study  of  a  given  system  of 
organs  with  the  lowest  forms  of  animal  life,  and  to  follow 
on  up  to  the  highest  mammals.  In  the  case  of  the  kidneys 
the  opposite  plan  seems  preferable.  Among  all  mammals 
the  kidneys  have  a  similar  position  and  structure,  and  con- 
sist of  cortical  and  medullary  regions,  the  latter  being  made 
up  of  separate  pyramids.  Birds  show  the  first  striking 
modification  in  kidney  structure,  for  in  this  group  the  cor- 
tex and  medullary  layer  cannot  be  distinguished.  Birds, 
too,  have  no  urinary  bladder,  and  the  ureters  empty  directly 
into  a  cavity  known  as  the  do-a'ca  (Latin  cloaca  =  a  sewer), 
into  which  opens  also  the  rectum.  The  urine  is  thus 
mingled  with  waste  food  substances  from  the  alimentary 
canal.  Among  reptiles,  amphibia,  and  fishes,  there  is  so 
much  diversity  of  structure  that  any  comparative  study  of 
excretion  is  impossible  within  a  limited  space. 

The  Kidneys  of  Invertebrates.  —  In  the  lobster  there  are 
two  so-called  green  glands  situated  in  the  head  region  near 
the  base  of  the  antennae,  and  these  act  as  kidneys,  since 
they  have  been  proved  to  excrete  urea.  Each  segment  of 
an  earthworm  has  a  pair  of  twisted  tubes  that  open  upon 
the  surface  of  the  body  (Fig.  38,  A).  These  are  of  use  in 
removing  urea  and  other  wastes.  Hence  an  earthworm  may 
be  said  to  have  twice  as  many  kidneys  as  it  has  segments. 
In  some  other  groups  of  invertebrates  organs  corresponding 
to  kidneys  have  not  been  identified. 


CHAPTER   XIII 

A  STUDY  OF  THE  NERVOUS  SYSTEM 

The  Body  as  a  Collection  of  Organs.  —  In  the  preceding 
chapters  we  have  discussed  the  digestive,  respiratory,  and 
circulatory  systems  and  have  seen  that  these  organs  furnish 
all  parts  of  the  body  with  food  and  oxygen.  We  have 
studied  the  process  of  oxidation  whereby  we  keep  warm 
and  get  power  to  do  work.  And,  finally,  we  have  consid- 
ered the  bones  and  muscles  as  the  organs  that  give  support 
to  the  body  and  provide  the  machinery  for  all  our  motions. 
The  fact  has  been  continually  emphasized  that  the  body  is 
composed  of  a  great  many  organs,  each  with  its  special 
function  or  functions. 

Cooperation  of  the  Organs.  —  But  a  human  being  or  any 
other  complex  organism  is  more  than  a  mere  collection  of 
working  organs.  In  our  definition  of  an  organism  (p.  39) 
we  included  the  statement  that  all  the  various  organs  work 
together  for  the  common  good.  This  is  what  we  mean  by 
cooperation  (Latin  co-  =  together  -+-  operari  =  to  work).  Sup- 
pose we  take  a  few  instances  from  everyday  experiences  to 
illustrate  this  cooperation. 

When  I  take  food  into  my  mouth,  my  salivary  glands 
pour  out  upon  it  an  abundant  supply  of  saliva.  Now,  the 
food  never  comes  in  contact  with  the  glands.  How  is  it, 
then,  that  they  send  out  their  secretion  at  just  the  right 
time  and  in  the  proper  amount  ?  The  same  questions  may 
be  asked  with  reference  to  the  gastric  and  pancreatic  secre- 
tions. If  any  one  attempts  to  strike  me  in  the  eye,  my 
eyelids  instantly  close,  and  my  hands  fly  up  in  front  of  my 
face  to  ward  off  the  blow. 

253 


254  STUDIES  IN  PHYSIOLOGY 

Or  let  us  take  a  more  complex  example  of  cooperation 
between  the  different  organs.  Suppose  I  am  a  batsman  on 
the  baseball  field,  and  a  ball,  thrown  by  the  pitcher,  is 
coming  swiftly  toward  me.  For  an  instant  I  wait  with 
every  muscle  rigid ;  then  my  arms  swing  the  bat  to  strike 
vigorously  at  the  passing  ball.  If  I  am  fortunate  enough 
to  make  a  hit,  my  hands  at  once  drop  the  bat,  and  my  legs 
begin  to  carry  me  swiftly  toward  first  base.  On  reaching 
this  goal,  if  I  stopped  to  consider  the  physiological  condi- 
tion of  my  body,  I  should  find  that  my  heart  was  pumping 
twenty  to  fifty  times  more  per  minute  than  it  was  when  I 
started ;  that  my  rate  of  breathing  was  more  rapid ;  and  that 
the  flow  of  perspiration  had  been  considerably  increased. 
I  should  doubtless  experience  a  feeling  of  satisfaction  that 
I  had  not  been  "  struck  out "  by  the  pitcher,  and  a  determi- 
nation to  complete  the  run  of  the  bases  and  thus  make  a 
score  for  my  team. 

Functions  of  the  Nervous  System.  —  All  the  succession  of 
activities  just  described  would  be  utterly  impossible  if  some 
means  were  not  provided  for  making  the  organs  work 
together  for  the  common  good.  The  arms  could  not  see 
to  strike  at  the  ball ;  the  legs  could  not  make  themselves 
run  toward  first  base ;  nor  could  the  heart,  lungs,  and  skin 
respond  to  the  sudden  exertion  of  the  rest  of  the  body.  It 
is  the  nervous  system  that  controls  the  action  of  each  of  the 
organs  in  our  body  and  brings  about  a  cooperation  between 
them.  All  our  sensations,  too,  and  our  will  power  are  doubt- 
less correlated  with  the  activities  of  the  nervous  system. 

Parts  of  the  Nervous  System.  —  The  nervous  system  may 
be  said  to  consist  of  nerve  centers  and  nerve  trunks.  The 
principal  nerve  centers  are  in  the  brain  and  spinal  cord. 
These  are  sometimes  said  to  constitute  the  central  nervous 
system  or  cer'e-bro-spi'nal  center  (Latin  cerebrum  =  brain). 
We  have  already  seen  that  these  delicate  organs  are  inclosed 
and  wonderfully  protected  by  the  bony  cranium  and  spinal 
column. 


A  STUDY   OF  THE  NERVOUS   SYSTEM 


255 


•^^w— 

FIG.  115.  —  Diagram  illustrating  the  General  Arrangement  of 
the  Nervous  System. 


256  STUDIES  IN  PHYSIOLOGY 

From  either  side  of  this  nerve  center  pass  off  numerous 
bundles  of  nerve  fibers;  these  are  sometimes  called  nerve 
trunks  or  simply  nerves.  As  they  approach  the  different 
organs  of  the  body  they  divide  into  branches,  and  thus  the 
nerves  become  smaller  and  smaller.  Finally,  the  microscope 
is  needed  to  trace  the  individual  nerve  fibers  to  their  end- 
ings in  muscle,  gland,  or  sense  organ.  By  means  of  these 
countless  nerve  fibers  all  parts  of  the  body  are  put  in  com- 
munication with  the  nerve  centers  (see  Fig.  115). 

Since  the  structure  and  functions  of  the  brain  are  exceed- 
ingly intricate  and  difficult  to  understand,  we  will  first 
study  the  least  complicated  part  of  the  cerebro-spinal  nerve 
center,  namely  the  spinal  cord. 

1.   ANATOMY  OF  THE  SPINAL  CORD 

Shape  and  Size.  —  The  spinal  cord  is  more  or  less  cylin- 
drical in  shape.  Its  length  in  an  adult  is  about  a  foot  and 
a  half.  If  one  measures  this  distance  posteriorly  from  the 
base  of  a  man's  head,  one  will  find  that  the  cord  terminates 
in  the  small  of  the  back  (near  the  first  lumbar  vertebra). 
Its  average  diameter  from  side  to  side  is  about  three- 
quarters  of  an  inch.  Since  its  dorsal  and  ventral  surfaces 
are  somewhat  flattened,  a  piece  of  the  cord  might  be  com- 
pared in  its  general  form  and  size  to  one's  little  finger. 

The  spinal  cord  is  not  of  the  same  size,  however,  through- 
out its  whole  extent.  In  the  lower  neck  region  its  diameter 
increases  considerably ;  this  is  the  so-called  cer'vi-cal  enlarge- 
ment. A  second  expansion,  the  lum'bar  enlargement,  occurs 
near  its  posterior  end.  These  two  enlargements  are  found 
where  collections  of  nerves  run  off  to  the  arms  and  the  legs. 
Posterior  to  the  lumbar  enlargement  the  cord  tapers  off  and 
ends  in  a  slender  thread  (see  Fig.  121). 

Fissures.  —  Along  the  ventral  surface  of  the  cord  runs  a 
deep  groove,  and  a  corresponding  though  much  shallower 
groove  furrows  the  dorsal  surface.  By  these  so-called  dorsal 


A  STUDY  OF  THE   NERVOUS   SYSTEM 


257 


Ventral  nerve-root 


and  ventral  fissures  the  spinal  cord  is  partly  divided  into 
right  and  left  halves  (see  Fig.  117). 

Coverings  of  the  Cord. — Three  distinct  coverings  surround 
the  cord.  The  outside  one  is  a  loose  sheath  of  tough  con- 
nective tissue ;  it  is  called  the  dura  mater  (Latin  dura  = 
hard  +  mater  =  mother,  probably  because  of  the  protec- 
tion it  affords). 
The  innermost  of 
the  three  mem- 
branes, the  pia 
mater  (Latin  pia 
=  gentle  +  mater 
=  mother),  is  a 
thin  covering, 
well  supplied  with 
blood  vessels,  and 
is  closely  at-  « 
tached  to  the  cord. 
Between  the  dura 
and  pia  mater  is 
a  third  layer  of 
loose  connective 
tissue  with  an 
appearance  some-  pa,urtorp,lin.ry- 
thing  like  that  Anterior^ 
of  a  spider's  web ; 

from  this  fact  it  is  FlG'  116>  ~~  Piece  of  sPinal  Cord,  showing  its  Three 

Coverings  and  the  Roots  of  the  Spinal  Nerves, 
called  the  a-rach1- 

noid  (Greek,  meaning  like  a  spider's  web).  Within  the 
meshes  of  the  arachnoid  is  a  watery  fluid  (cerebro-spinal 
fluid)  somewhat  like  lymph  in  composition.  The  spinal 
cord,  then,  is  successively  wrapped  about  and  protected  by 
the  following  coverings,  —  skin,  muscle,  bony  arches  of  the 
vertebrae,  dura  mater,  arachnoid  with  its  liquid,  and  pia 
mater. 

Cross  Section  of  the  Cord.  —  When  one  looks  at  the  cross 


Dorsal  nerve-root 


Dorsal  ganglion 


'«ntr»l  nerve-raot 


Spinal  cord 


258 


STUDIES   IN  PHYSIOLOGY 


section  of  the  cord,  apparently  two  kinds  of  material,  known 
as  gray  and  white  matter,  can  be  distinguished.  In  the  interior 
of  the  cord  is  the  gray  matter  in  a  form  somewhat  resembling 
that  of  a  capital  H.  The  two  projections  of  the  H  that 
extend  toward  the  ventral  face  of  the  spinal  cord  are  called 
the  ventral  horns  of  the  gray  matter ;  the  two  dorsal  horns 
extend  in  the  opposite  direction  to  the  outer  surface  of  the 
cord.  Running  across  the  cord  and  connecting  the  two 
halves  is  a  bridge  of  gray  matter,  the  gray  coin' mis-sure. 

The      H -shaped 

A tfferefi '/ r/erres  to 
vcf 

faffer* 


Oorsa/  fissure 


Centra/ 
f/ssure 


fiferert  serves  from 
spincr/cortf 


mass  of  gray 
matter  is  sur- 
rounded by  the 
white  matter 
which  consti- 
tutes the  re- 
mainder of  the 
cord. 

Nerve  Cells 
and  Fibers. — 
TJie  unit  of  struc- 
ture in  the  nerv- 
ous system,  as 
in  other  tissues 

of  the  body,  is  the  cell  with  its  processes.  Nerve  cells,  how- 
ever, are  more  varied  in  form  and  more  complex  in  structure 
than  any  other  cells  in  the  body.  When  the  ventral  horns 
of  the  gray  matter  are  sufficiently  magnified,  one  sees  irregu- 
lar bits  of  protoplasm,  shaped  more  or  less  like  triangles  or 
polygons.  From  the  angles  of  each  cell  body  project  numer- 
ous fine  processes  that  look  like  tiny  branching  roots.  These 
are  the  protoplasmic  processes.  Another  fiberlike  process,  how- 
ever, has  fewer  branches  than  the  others,  and  can  be  traced 
for  a  considerable  distance  from  the  cell  body.  This  is 
called  an  axis  cylinder  process ;  it  is  the  beginning  of  a  nerve 
fiber.  A  short  distance  from  the  cell  body  the  axis  cylinder 


FIG.  117.  —  Diagram  of  Cross  Section  of  Spinal  Cord. 

Showing  the  H-shaped  gray  matter,  inclosed  within 
the  white  matter.  Also  a  diagrammatic  represen- 
tation of  the  afferent,  efferent,  and  connecting 
fibers  used  in  reflex  action. 


A   STUDY  OF  THE   NERVOUS   SYSTEM 


259 


becomes  surrounded  by  a  thick  covering,  called  the  med'ul-la-ry 
sheath.  Nerve  fibers  outside  the  spinal  cord  are  covered  by 
a  very  thin  outer  membrane,  known  as  the  prim'i-tive  sheath. 
(A  common  lead  pencil 
might  be  used  to  present 
to  the  eye  the  structure 
of  such  a  nerve  fiber. 
The  "lead"  or  graphite 
in  the  center  of  the  pen- 
cil corresponds  in  posi- 
tion and  form  to  the  axis 
cylinder  of  the  nerve 
fiber ;  the  wood  surround- 
ing the  lead  answers  to 
the  medullary  sheath ; 
and  the  thin  layer  of 
paint  or  varnish  on  the 
outside  of  the  pencil  rep- 
resents the  primitive 
sheath  of  the  nerve.) 

In  all  parts  of  the  gray 
matter  we  find  nerve 
cells.  While  they  vary  greatly  in  form  and  size,  almost  all 
have  a  cell  body  with  protoplasmic  processes  and  a  single  axis 
cylinder  process.  These  axis  cylinders,  usually  after  a  more 
or  less  tortuous  course,  divide  into  very  fine  branches  and 


FIG.  118.  — Branched  Nerve  Cell  from 
Spinal  Cord. 

a  =  long  axis  cylinder. 
'  6  =  branching  protoplasmic  processes, 
c  =  supporting  tissue. 


FIG.  119.  —  Medullated  Nerve  Fiber. 

In  the  center  is  the  axis  cylinder.  The  black  lines  on  either  side  repre- 
sent the  medullary  sheath.  On  the  outside  represented  in  white  is  the 
thin  primitive  sheath  in  which  is  a  nucleus. 

thus  form  a  so-called  terminal  brush.  We  shall  find  that 
these  cells  and  fibers  perform  the  important  function  of 
connecting  or  coordinating  the  various  parts-  of  the  cord. 


260 


STUDIES   IN  PHYSIOLOGY 


Fia.    120.  —  Portion  of    Spinal    Cord, 
magnified  30  times. 

Photographed  through  the  microscope. 
Upper  three  fourths  of  photograph  is 
gray  matter  containing  nerve  cells 
(irregular  black  spots),  with  their 
processes  and  axis  cylinders  (black 
dots  and  lines) .  Lower  fourth  of  pic- 
ture is  white  matter,  showing  five 
bundles  of  nerve  fibers.  Between 
these  bundles  are  seen  the  cross  sec- 
tions of  axis  cylinders  (small  black 
dots),  each  surrounded  by  medullary 
sheath  (white  circle) . 


Nerve  cells  and  proto- 
plasmic processes  are  gray 
in  color,  and  since  they 
constitute  the  most  impor- 
tant part  of  the  gray  mat- 
ter of  the  nervous  system, 
they  give  the  latter  its 
characteristic  shade.  The 
white  color  of  the  outer 
portion  of  the  spinal  cord 
is  due  to  the  presence 
of  the  medullary  sheaths, 
which  in  a  fresh  condi- 
tion are  white  and  glis- 
tening. 

Among  the  nerve  cells 
and  fibers  one  finds  a  tis- 
sue similar  to  connective 
tissue  and  numerous  blood 
vessels ;  the  former  serves 
as  a  supporting  frame- 
work, the  latter  bring  the 
nutrients  and  oxygen  that 
are  necessary  for  nervous 
metabolism. 


2.   ANATOMY  OF  THE  SPINAL  NERVES 

Number  of  Nerves.  —  While  studying  the  skeleton  we 
called  attention  to  a  row  of  holes  on  either  side  of  the 
spinal  column.  Through  these  openings  between  the  verte- 
brae (intervertebral  foramina)  there  pass  laterally  from  the 
spinal  cord  the  spinal  nerves,  of  which  there  are  thirty-one 
pairs.  These  are  arranged  in  five  groups,  named  accord- 
ing to  the  region  of  the  vertebral  column  from  which  they 
make  their  exit.  The  following  table  shows  the  relation 


A  STUDY  OF  THE  NERVOUS  SYSTEM 


261 


between  the  number  of  nerves  and  the  number  of  vertebrae 
in  each  region :  — 


NUMBER  OF 

NAME  OF  EEGION 

PAIRS  OF  NERVES 

NUMBER  OF  VERTEBRA 

Cervical    . 

8 

7 

Dorsal 

12 

12 

Lumbar    . 

5 

5 

Sacral 
Coccygeal 

5 
1 

5  (united  into  one) 
4  (united  into  one) 

Total 

31 

33  (child)  26  (adult) 

Distribution  of  Nerves.  —  Five  of  the  nerves  on  each  side 
that  come  from  the  cervical  enlargement,  after  uniting  more 
or  less  with  each  other,  pass  down  the  arm,  supplying  its 
various  muscles  and  sense  organs.  To  the  hips  and  the 
legs,  likewise,  are  distributed  most  of  the  nerves  from  the 
lumbar  enlargement.  All  the  spinal  nerves,  after  their  exit 
from  the  spinal  column,  divide  into  smaller  and  smaller 
branches,  and  these  reach  all  parts  of  the  trunk  and  the 
appendages  (see  Fig.  115). 

Origin  of  the  Nerves.  —  Each  spinal  nerve  arises  from  the 
cord  by  two  so-called  roots.  From  the  dorsal  surface  of  the 
spinal  cord  on  each  side,  a  white  nerve  trunk  passes  outward 
to  form  the  dorsal  root  of  the  nerve.  Strands  of  fibers  that 
originate  in  the  gray  ventral  horn  unite  to  form  the  ventral 
root.  These  two  roots  come  together  within  the  bony  cavity 
of  the  spinal  column,  forming  the  spinal  nerve  which  we 
have  followed  out  through  a  hole  between  the  vertebrae  to 
its  destination  in  the  tissues  (see  Figs.  116  and  117). 

Structure  of  a  Spinal  Nerve. —  In  the  cross  section  of  a 
spinal  nerve  one  sees  that  the  whole  nerve  trunk  is  sur- 
rounded by  connective  tissue.  Within  this  outside  sheath 
the  nerve  fibers  are  collected  into  bundles,  and  each  bundle 
is  inclosed  by  a  covering  of  connective  tissue,  called  per'i- 


262 


STUDIES  IN  PHYSIOLOGY 


•S 


neu'ri-um    (Greek  peri  =  around  +  neuron  =  nerve.) l     And 
finally,  each  fiber  consists  of  an  axis  cylinder  wrapped  up 

in  the  medullary  and 
primitive  sheaths. 
Now,  the  essential 
part  of  every  nerve 
fiber  is  its  axis  cylin- 
der, for  this  carries 
the  nerve  impulse 
from  the  cell  body  to 
another  cell  with 
which  it  is  connected. 
Hence  a  nerve  trunk 
may  be  compared  to 
a  cable  composed  of 
separate  bundles  of 
telegraph  wires,  in 
which  each  individual 
wire  (corresponding 
to  the  axis  cylinder 
of  a  nerve)  is  sepa- 
rated or  insulated  by 
its  covering  from  its 
neighbor  (Fig.  122). 

Structure  of  a  Spinal 
*  |  f  -3  §  Ganglion.  —  The  dor- 
1? "I,  U '§  §  sal  root  of  every 
&  §  8  •§  spinal  nerve  has  an 
i  -  <»  jl  enlargement,  called 
^3  a  spinal  gan'gli-on 
$  <=$  (Greek  ganglion  =  a 

•o  swelling).     These 

ganglia  are  very  small 
nerve  centers,  and  consist  largely  of  nerve  cells.     Many  of 

i  In  much  the  same  way  the  smaller  bundles  of  muscle  are  sur- 
rounded and  held  together  by  the  connective  tissue  called  perimysium. 


S£  I  .^ 

"2 1  | 


A  STUDY  OF  THE  NERVOUS   SYSTEM  263 

these  nerve  cells,  however,  have  two  long  processes :  one 
comes  in  along  the  nerve 
trunk  from  the  organs  of 
the  body,  the  other  runs 
from  the  ganglion  into  the 
dorsal  part  of  the  cord, 
ending  at  length  in  a  ter-  / 
minal  brush  like  those  al- 
ready described  (Fig.  117). 
Relation  of  Cells  and 
Fibers. — The  nervous  sys- 
tem, then,  is  made  up  of  a 
very  great  number  of  dis-  FlG-  122. -Cross  Section  of  Nerve 

tinct    units,    called    nerve  c 

.  Snowing  smaller  bundles  ot  nerve  fibers 

cells.    The  I'OOtlike  processes       surrounded    by    connective    tissue, 
that     reach    out    from    the        Magnified    6   times.      Photographed 
, ,      ,      , .  iii  •  ->        through  the  microscope. 

cell    bodies    probably    aid 

in  bringing  about  cooperation  between  the  various  cells  in 
a  nerve  center.  And  finally,  the  long  axis  cylinder  which 
extends  from  each  nerve  cell  serves  like  a  telegraph  wire  to 
connect  the  distant  muscle  or  skin  with  the  central  nerve 
station.  The  length  of  these  slender  axis  cylinders  some- 
times measures  several  feet,  as  is  the  case  with  those  which 
run  from  the  spinal  cord  to  the  tips  of  the  toes 

3.   PHYSIOLOGY  OF  THE  SPINAL  CORD  AND  SPINAL  NERVES 

Experiments  on  Animals.  —  The  functions  of  various  parts 
of  the  nervous  system  have  been  determined  to  a  large  ex- 
tent by  experiments  performed  on  animals.  When  a  dog, 
for  instance,  is  given  ether,  it  is  made  insensible  to  pain, 
and  the  large  nerve  trunks  that  supply  one  of  the  front  legs 
may  then  be  severed  near  the  shoulder.  On  recovering  from 
the  effects  of  the  ether,  the  animal  is  found  to  have  lost  all 
sensation  and  all  power  of  movement  in  this  leg.  But  when 
the  cut  ends  of  the  nerves  are  brought  into  contact  and  the 


264  STUDIES   IN  PHYSIOLOGY 

nerve  is  allowed  to  grow  again,  the  dog  recovers  the  sense 
of  feeling  in  its  leg  and  is  able  to  move  It  at  will. 

In  a  second  animal  we  may  cut  only  the  dorsal  roots  of 
the  nerves  to  the  front  leg,  severing  these  roots  between 
the  cord  and  the  spinal  ganglia.  The  dog  is  still  able  to 
move  its  leg,  as  usual.  But  if  the  paw  is  pinched,  or  even 
burned,  the  animal  shows  no  sign  that  it  feels  any  pain. 
When,  on  the  other  hand,  only  the  ventral  roots  of  these 
spinal  nerves  are  cut,  the  dog  loses  all  control  over  the  mus- 
cles of  its  leg.  Let  the  paw  now  be  pinched,  however,  and 
the  animal  at  once  gives  unmistakable  signs  of  discomfort. 

Functions  of  Nerve  Fibers. — Experiments  like  those  just 
described  prove  beyond  a  doubt  that  the  nerve  impulses  that 
result  in  sensation  or  in  motion  are  carried  by  nerve  fibers. 
It  is  evident,  too,  that  the  dorsal  and  ventral  roots  of  spinal 
nerves  differ  in  their  function.  We  saw  that  sensation  was 
destroyed  by  cutting  the  nerve  fibers  that  enter  the  dorsal 
horns  of  the  gray  matter.  Hence,  we  conclude  that  the 
fibers  in  the  dorsal  roots  carry  messages  to  the  spinal  cord, 
and,  because  they  have  this  function,  we  call  them  af'fer-ent 
fibers  (Latin  ad  =  to  -\-ferre  =  to  carry).  By  the  last  ex- 
periment described  above  we  proved  that  the  ventral  roots 
conduct  messages  from  the  cord  to  the  muscles;  these  nerve 
fibers  are  therefore  known  as  ef'fer-ent  (Latin  ex  =  from  -f 
ferre  =  to  carry)  (see  Fig.  117). 

Nerve  Impulses.  —  We  have  liken  }d  nerve  fibers  to  tele- 
graph wires,  and  nerve  impulses  have  been  described  as 
messages  that  pass  along  the  axis  cylinders.  But  in  mak- 
ing these  comparisons  we  must  remember  that  telegraphy 
and  the  action  of  the  nervous  system  have,  in  all  probabil- 
ity, little  real  resemblance.  We  know  that  nerves  transmit 
impulses  at  the  rate  of  about  one  hundred  feet  per  second ; 
electricity  travels  thousands  of  miles  per  second.  Hence  a 
nerve  impulse  cannot  very  closely  resemble  what  we  call 
a  telegraph  message.  On  the  other  hand,  this  nerve  im- 
pulse travels  much  too  rapidly  to  be  explained  as  a  chem- 


A   STUDY   OF   THE   NERVOUS   SYSTEM  265 

ical  or  mechanical  action.  We  must  therefore  admit  our 
ignorance  of  the  real  nature  of  the  nervous  impulse  that 
passes  along  the  axis  cylinders ;  nor  do  we  know  the  real 
nature  of  the  changes  that  take  place  in  the  nerve  cells 
after  receiving  the  so-called  message. 

Reflex  Action.  —  To  get  an  idea  of  the  action  of  our  own 
complicated  system  of  nerve  cells  and  fibers,  let  us  consider 
the  common  experience  of  burning  one's  finger.  If  I  acci- 
dentally touch  a  hot  stove,  my  hand  is  withdrawn  instantly, 
and  afterward  I  feel  the  pain  of  the  burn.  This  uncon- 
scious and  automatic  withdrawal  of  the  hand  is  called  a 
reflex  action.  We  will  now  try  to  explain  this  'action  from 
what  we  have  learned  of  the  structure  of  the  spinal  cord 
and  its  nerves  (see  Fig.  117). 

By  following  the  afferent  fibers  outward  from  the  spinal 
cord,  we  find  that  some  of  them  terminate  in  the  dermis 
of  the  hand.  When  I  touch  the  hot  stove,  these  fiber  termi- 
nations in  my  hand  are  roused  by  the  stimulus  of  the  heat 
into  some  kind  of  activity.  The  impulse  thereby  aroused 
is  conducted  up  my  arm  along  the  axis  cylinders  of  the 
afferent  fibers,  and  soon  reaches  the  cells  in  the  ganglia  of 
the  dorsal  roots;  thence  it  passes  along  the  second  axis 
cylinder  from  each  of  these  ganglion  cells,  and  finally 
reaches  the  terminal  brushes  in  the  gray  matter  of  the 
cord.  From  this  region  a  stimulus  is  transmitted  in  two 
directions.  In  the  first  place  the  cells  in  the  ventral  horn 
are  at  once  aroused,  and  a  message  is  sent  out  along  the 
efferent  fibers  of  the  ventral  roots  to  the  muscles  of  my 
arm.  The  muscles  contract,  and  my  hand  is  pulled  away 
from  the  hot  stove.  All  the  events  we  have  been  describ- 
ing occur  almost  instantly  and  are  carried  on  without  any 
action  on  the  part  of  the  brain. 

While  the  nerve  impulse  is  being  rushed  from  the  cord 
out  to  the  muscles,  a  second  message  is  hurrying  through  the 
white  matter  of  my  spinal  cord  toward  my  brain.  These 
fibers  finally  terminate  in  the  so-called  sen'so-ry  cells  of  the 


266 


STUDIES  IN  PHYSIOLOGY 


brain.  Not  until  the  message  reaches  these  cells  am  I  con- 
scious that  I  have  been  burned.  Fortunately,  however,  my 
hand  has  already  been  removed  from  danger. 


JVoter  ct/t  of 

,.-'    cerebral  cortex 

>''~,~  'Ce// of  cortex  of 
<•"  cfrefira/n 


ffferent  newe-  -  - 
from  cerebrum 


Cere0e//(/m 

Jfferentrterre 

to  cerebrum 


— Afferent  nerve  to 
cere6e//un? 


Afferent  rtery& 
fro/n  sfl/na/ co    ' 


r  -  -Afferent  r?erre 
to  spjra/coraf 


FIG.  123.  — Diagram  to  illustrate  Cells  and  Afferent,  Efferent,  and  Connect- 
ing Fibers  of  Brain  and  Spinal  Cord. 

Many  other  activities  of  the  body,  as  we  shall  soon  learn, 
are  carried  on  in  a  reflex  manner  similar  to  that  already 
described,  and  are  executed  entirely  without  our  conscious 
effort. 

4.   THE  SYMPATHETIC  NERVOUS  SYSTEM 

Anatomy.  —  Closely  associated  with  the  spinal  nerves  is 
the  sympathetic  nervous  system.  It  consists  of  a  number  of 
gray  ganglia,  the  nerve  cells  of  which  are  connected  by  gray 
nerve  fibers  (fibers  without  the  medullary  sheath).  Most  of 
the  sympathetic  ganglia  are  strung  together  in  two  parallel 
chains  that  extend  along  either  side  of  the  spinal  column 


A  STUDY  OF  THE   NERVOUS   SYSTEM 


267 


from  the  base  of  the  skull  to  the  coccyx, 
the  stomach  is  a  large  mass 
of  nerves  and  ganglia  known 
as  the  solar  plexus,  and  still 
other  masses  of  this  gray  nerve 
tissue  are  found  near  the  vari- 
ous organs  in  the  chest  and 
abdomen.  Branches  from  the 
spinal  nerves  connect  the 
sympathetic  ganglia  with  the 
gray  matter  of  the  cord  and 
brain,  and  from  the  ganglia 
there  pass  off  a  great  number 
of  nerve  fibers  that  supply  the 
organs  of  digestion,  respira- 
tion, and  circulation.  • 

Physiology.  —  The  vital  or- 
gans just  mentioned  carry  on 
their  work  without  any  con- 
scious direction  on  our  part. 
When  the  stomach  receives 
food  from  the  mouth,  the  pan- 
creas begins  to  secrete  more 
rapidly  the  juice  that  will  be 
needed  to  act  upon  this  food  in 
the  intestines ;  during  diges- 
tion the  muscles  of  the  abdomi- 
nal arteries  relax,  thus  allow- 
ing a  greater  blood  supply  in 
the  walls  of  the  alimentary 
canal;  violent  exercise  quick- 
ens the  action  of  the  heart, — 
these  and  many  other  activi- 
ties of  the  body  are  controlled 
either  directly  by  the  sym- 
pathetic ganglia  or  indirectly 


In  the  region  of 


.  124.  —  Diagram  of  Sympathetic 
System  on  One  Side  of  Body. 

1  =  ganglia  and  nerve  sup- 

plying    heart  =  car- 
diac plexus. 

2  =  solar  plexus  (for  stom- 

ach and  other  organs 
of  ahdomen). 

3  =  hypogastric  plexus  (for 

organs  of  pelvic  re- 
gion). 

4,  5,  6,  7  =  row    of    ganglia    near 
spinal  column. 


268  STUDIES  IN  PHYSIOLOGY 

by  impulses  sent  out  from  the  brain  and  spinal  cord.  This 
part  of  our  nervous  machinery  is  called  the  sympathetic 
system  because  its  cells  and  fibers  make  the  various  involun- 
tary muscles  of  the  body  work  in  harmony  or  sympathy 
with  each  other. 


5.   THE  NERVOUS  SYSTEM  OF  A  FROG 

Reason  for  studying  Frog's  Brain.  —  We  have  stated  that 
the  human  brain  has  a  very  complicated  structure.  This 
is  less  true  of  the  central  nervous  system  of  other  animals. 
For,  in  comparing  the  nervous  systems  of  various  kinds  of 
vertebrates,  one  finds  that  in  the  lower  groups  the  brain  is 
considerably  more  simple.  Such  a  brain  has  the  frog,  and 
the  study  of  the  central  nervous  system  of  the  frog  will  help 
much  toward  a  comprehension  of  the  structure  and  functions 
of  the  human  brain. 

The  frog's  brain,  like  that  of  the  human  being,  is  a  con- 
tinuation of  the  spinal  cord  inclosed  within  a  bony  cranium. 
Three  regions  may  be  distinguished:  the  forebrain,  the 
midbrain,  and  the  hindbrain. 

Forebrain.  —  The  forebrain  consists  principally  of  two 
elongated  masses  called  the  cer'e-bral  hemispheres.  Nerve 
fibers  run  in  from  the  sensory  cells  of  the  nose  to  the 
anterior  part  of  these  cerebral  hemispheres,  and  carry  to 
the  brain  the  impulses  that  give  to  the  animal  the  sense 
of  smell.  For  this  reason  these  nerve  trunks  are  known 
as  ol-fac'to-ry  nerves  (Latin  olfactus  —  smell),  and  the  portion 
of  the  hemispheres  with  which  they  connect  are  called  the 
olfactory  lobes. 

Midbrain.  —  Two  prominent  enlargements  cover  the  top 
and  sides  of  the  midbrain.  They  are  called  the  op' tic  lobes 
(Greek  optikos}  relating  to  sight),  from  the  fact  that  the 
large  nerves  from  the  eyes  enter  them.  On  the  ventral 
surface  of  the  brain  these  two  optic  nerves  cross  each  other, 
the  nerve  fibers  from  the  right  eye  passing  to  the  left  optic 


A   STUDY   OF  THE   NERVOUS   SYSTEM 


269 


lobe,  while  those  from  the  left  eye  go  to  the  right  lobe. 
These  fibers  finally  communicate  with  cells  in  the  forebrain. 

Hindbrain.  —  Extending  across  the  dor- 
sal surface  of  the  hindbrain  just  behind 
the  optic  lobes  is  a  ridge  of  brain  tissue 
called  the  cer-e-bel'lum  (Latin  cerebellum 
=  little  brain).  To  the  remainder  of 
the  hindbrain  is  given  the  name  me- 
dul'la  ob-lon-ga'ta  (Latin  medulla  = 
marrow  -f-  oblongata  =  oblong).  Seven 
pairs  of  nerves  are  connected  with  the 
medulla.  The  third  (arising  from  mid- 
brain),  fourth,  and  sixth  pairs  are  dis- 
tributed to  the  muscles  that  move  the  _, 

FIG.  125.  —  Dorsal  View 

eyeballs.     The  fifth  and  seventh  nerves        of  Frog's  Brain. 

bring  to  the  brain  messages  from  the 

sense  organs   in  the  skin  and  mucous 

membrane  of  the  head  region,  and  carry 

impulses  from  the  brain  to  the  muscles 

of  the  jaws  and  eyelids  and  face.     The 

eighth  pair  of  nerves,  called  au'di-to-ry 

(Latin   audire  =  to  hear),  connect   the 

ear   with   the  brain.      The    ninth   pair 

supply  the  tongue   and   pharynx,   and 

hence    are    called    glos'so-phar-yn-ge'al 

(Greek  glossa  =  tongue  +  pharyngeal  =  v>  VII  =  fifth  and  sev- 

referring  to  the  throat).     The  distribu-  nerve^8  °f 

tion  of  the  tenth  pair  of  nerves  is  the      VIII  =  eighth      pair 

widest  of  any  of  the  brain  or  cranial  i*™*0^ 

nerves,  and  for  this  reason  it  has  been   ix,  x=  ninth       and 

named  the  va'qus  (Latin,  vagus  =  wan-  tenth    Pairs 

i     •      \       -r,      01  -,.  ;  -i     ,    i  of  nerves, 

dering).     Its  fibers   are   distributed   to 

the  lungs  and  air  passages,  to  the  heart  and  blood  vessels, 
and  to  the  organs  of  digestion. 

The  Spinal  and  Sympathetic  Nerve  Systems.  —  The  posterior 
end  of  the  medulla  is  continuous  with  the  cylindrical  spinal 


HH=  cerebellum. 

Lol  =  olfactory 
lobes. 

Med  —  spinal  cord. 

MH  =  midbrain  (op- 
tic lobes). 

NH  =  medulla  ob- 
longata. 

VH  =  forebrain  (cer- 
ebral hemi- 
spheres) . 

J=first  pair 
(olfactory) 
nerves. 


270 


STUDIES  IN  PHYSIOLOGY 


cord.  Ten  pairs  of  spinal  nerves  branch  off  from  the  cord 
and  are  distributed  to  all  parts  of  the  trunk.  Three  of  these 
pairs  (the  first,  second,  and  third)  are  distributed  to  the 
arms ;  the  legs  are  supplied  by  the  last  four  pairs.  From 
each  of  the  spinal  nerves,  branches  connect  with  the  chains 
of  sympathetic  ganglia  which  lie  on  the  dorsal  wall  of  the 
body  cavity.  Hence,  in  general  plan 
there  is  a  close  resemblance  between 
the  nervous  system  of  a  frog  and  that 
of  man  (compare  Figs.  121  and  126). 

Summary.  —  For  convenience  we 
have  described  the  central  nervous  sys- 
tem as  though  it  were  made  up  of  two 
distinct  parts,  brain  and  spinal  cord, 
each  having  its  separate  set  of  nerves. 
In  reality  there  is  no  such  division. 
We  must  rather  consider  the  brain  as 
a  prolongation  and  modification  within 
the  head,  of  the  spinal  cord.  In  the 
region  of  the  hindbrain  this  cylindrical 
rod  or  rather  tube  of  nerve  tissue  is 
enlarged  to  form  the  medulla  and  cere- 
bellum •;  farther  forward  are  the  two 
FIG.  126.  —  Ventral  View  enlargements  of  the  midbrain,  namely, 
^e  optic  lobes;  while  the  greatest 
expansion  is  noticed  in  the  cerebral 
hemispheres  and  olfactory  lobes  of 
the  forebrain. 

Each  of  the  ten  spinal  nerves  has  a 
dorsal  and  ventral  root,  and  is  therefore  composed  cf  both 
afferent  and  efferent  fibers.  The  ten  cranial  nerves  may  be 
arranged  in  three  groups :  the  first  (olfactory),  the  second 
(optic),  and  the  eighth  (auditory)  pairs  always  carry  mes- 
sages to  the  brain,  and  are  therefore  afferent;  the  third, 
fourth,  and  sixth  are  efferent,  since  they  convey  impulses  to 
the  eye  muscles  j  the  four  other  pairs  (fifth,  seventh,  ninth, 


Spinal  Cord,  and  Sym- 
pathetic System. 

I-X=  cranial  nerves. 
1-10  =  spinal  nerves. 


A   STUDY   OF  THE   NERVOUS   SYSTEM  271 

and  tenth)  are  both  afferent  and  efferent  (or  mixed  nerves) 
and  in  this  respect  resemble  the  spinal  nerves. 

Frog  Physiology.  —  We  are  probably  indebted  to  the  com- 
mon frog  more  than  to  any  other  animal  for  our  knowledge 
of  general  physiology.  Countless  experiments  have  been 
performed  upon  its  skin,  its  muscles,  its  sense  organs,  and 
its  central  nervous  system.  Some  of  these  experiments 
which  throw  light  upon  the  functions  of  the  various  parts 
of  the  brain  and  spinal  cord  will  now  be  described.1 

Functions  of  the  Spinal  Cord.  — When  we  separate  the  whole 
brain  from  the  spinal  cord  by  making  a  cut  just  behind  the 
medulla,  the  "  frog  will  still  continue  to  live,  but  with  a  very 
peculiarly  modified  activity.  It  ceases  to  breathe  or  swal- 
low; it  lies  flat  on  its  belly>  and  does  not,  like  a  normal 
frog,  sit  up  on  its  fore  paws,  though  its  hind  legs  are  kept, 
as  usual,  folded  against  its  body,  and  immediately  resume 
this  position  if  drawn  out.  If  thrown  on  its  back,  it  lies 
there  quietly,  without  turning  over  like  a  normal  frog. 
Locomotion  and  voice  seem  entirely  abolished.  If  we 
suspend  it  by  the  nose,  and  irritate  different  portions  of 
the  skin  by  acid,  it  performs  a  set  of  remarkable  ( defensive' 
movements  calculated  to  wipe  away  the  irritant.  Thus,  if 
the  breast  be  touched,  both  fore  paws  will  rub  it  vigorously  ; 
if  we  touch  the  outer  side  of  the  elbow,  the  hind  foot  of  the 
same  side  will  rise  directly  to  the  spot  and  wipe  it." 

Functions  of  the  Hindbrain  and  Midbrain.  —  "If,  in  a 
second  animal,  the  cut  be  made  just  behind  the  optic  lobes 
so  that  the  cerebellum  and  medulla  oblongata  remain  at- 
tached to  the  cord,  then  swallowing,  breathing,  crawling, 
and  a  rather  enfeebled  jumping  and  swimming  are  added  to 
the  movements  previously  observed.  .  .  /  The  animal, 
thrown  on  his  back,  immediately  turns  over  to  his  belly." 
If  the  cut  be  made  on  another  frog  just  in  front  of  the  optic 
lobes,  "  the  locomotion  both  on  land  and  water  become  quite 

1  In  this  account  we  shall  quote  from  a  most  interesting  book  by 
Professor  William  James  ('« Psychology,"  Vol.  I.  Henry  Holt  &  Co.> 


272  STUDIES  IN  PHYSIOLOGY 

normal,  and  in  addition  to  the  reflexes  already  shown  by 
the  lower  centers,  he  croaks  regularly  whenever  he  is 
pinched  under  the  arms." 

Effect  of  removing  the  Cerebral  Hemispheres.  —  "  A  frog  which 
has  lost  his  cerebral  hemispheres  alone  is  by  an  unpracticed  ob 
server  indistinguishable  from  a  normal  animal.  Not  only  is 
he  capable,  on  proper  instigation,  of  all  the  acts  already 
mentioned,  but  he  guides  himself  by  sight,  so  that  if  an 
obstacle  be  set  up  between  himself  and  the  light,  and  he  be 
forced  to  move  forward,  he  either  jumps  over  it  or  swerves 
to  one  side.  .  .  .  He  is,  in  short,  so  similar  in  every  re- 
spect to  a  normal  frog  that  it  would  take  a  person  very 
familiar  with  these  animals  to  suspect  anything  wrong  or 
wanting  with  him ;  but  even  then  such  a  person  would  soon 
remark  the  almost  entire  absence  of  spontaneous  motion  — 
that  is,  motion  unprovoked  by  any  present  incitation  of 
sense.  The  continued  motions  of  swimming,  performed 
by  the  creature  in  the  water,  seem  to  be  the  fatal  result  of 
the  contact  of  that  fluid  with  the  skin.  They  cease  when  a 
stick,  for  example,  touches  his  hand.  ...  He  manifests 
no  hunger,  and  will  suffer  a  fly  to  crawl  over  his  nose 
unsnapped  at.  Fear,  too,  seems  to  have  deserted  him." 

Functions  of  the  Cerebral  Hemispheres.  — "  But  now  if  to 
the  lower  centers  we  add  the  cerebral  hemispheres,  or  if, 
in  other  words,  we  make  an  intact  animal  the  subject 
of  our  observations,  all  this  is  changed.  .  .  .  Our  frog 
now  goes  through  long  and  complex  acts  of  locomotion 
spontaneously,  or  as  if  moved  by  what,  in  ourselves,  we 
would  call  an  idea.  His  reactions  to  outward  stimuli  vary 
their  form  too.  Instead  of  making  simple  defensive  move- 
ments with  his*  hind  legs,  like  a  headless  frog  if  touched ; 
or  of  giving  one  or  two  leaps  and  then  sitting  still  like  a 
hemisphereless  one,  he  makes  persistent  and  varied  efforts 
of  escape,  as  if,  not  the  mere  contact  of  the  physiologist's 
hand,  but  the  notion  of  danger  suggested  by  it  were  now 
his  spur.  Led  by  the  feeling  of  hunger,  too,  he  goes  in 


A   STUDY  OF  THE   NERVOUS   SYSTEM  273 

search  of  insects,  fish,  or  smaller  frogs,  and  varies  his  pro- 
cedure with  each  species  of  victim.  The  physiologist  can- 
not, by  manipulating  him,  elicit  croaking,  crawling  up  a 
board,  swimming,  or  stopping  at  will.  His  conduct  has 
become  incalculable — we  can  no  longer  foretell  it  exactly. 
Effort  to  escape  is  his  dominant  reaction,  but  he  may  do 
anything  else,  even  swell  up  and  become  perfectly  passive 
in  our  hands." 

Summary.  —  From  all  these  experiments  we  conclude 
(1)  that  the  cells  and  fibers  of  the  spinal  cord  are  able  to 
direct  reflex  movements  of  a  defensive  kind,  without  any 
help  from  the  brain ;  (2)  that  the  hind-  and  midbrains  con- 
trol the  processes  of  locomotion,  swallowing,  breathing,  and 
croaking;  and  (3)  that  all  the  voluntary  actions  of  the 
animal  are  governed  by  the  f  orebrain.  It  is  probable,  too, 
that  all  the  messages  which  come  in  from  the  eyes,  ears, 
nose,  and  skin  reach  the  forebrain  before  the  frog  experi- 
ences any  kind  of  sensation. 

6.   ANATOMY  OF  THE  HUMAN  BRAIN 

Protection  for  the  Brain.  —  The  human  brain  is  an  exceed- 
ingly delicate  mechanism,  and  would  be  liable  to  frequent 
injury  were  it  not  well  protected.  In  the  first  place,  the 
thick  growth  of  hair  and  the  loose,  tough  scalp  form  out- 
side coverings  for  the  head,  which  help  to  deaden  the  force 
of  possible  blows.  Again,  the  arched  form  of  the  cranium 
and  its  several  layers  of  bone  tissue  (two  layers  of  hard 
bone  separated  by  spongy  bone)  give  to  this  brain  case 
the  greatest  possible  elasticity  and  strength.  In  the  third 
place,  the  springiness  of  the  curved  spinal  column  and  of 
the  arched  instep  tends  to  keep  the  delicate  structures 
within  the  skull  from  being  jarred.  And,  finally,  the  brain 
itself  is  inclosed  by  the  dura  mater,  arachnoid,  and  pia 
mater,  which  are  continuous  with  the  corresponding  mem- 
branes about  the  cord. 


274 


STUDIES  IN  PHYSIOLOGY 


Parts  of  the  Brain.  —  The  human  brain,  like  that  of  the 
frog,  may  be  divided  into  three  regions,  the  forebrain, 
the  midbrain,  and  the  hindbrain.  The  hindbrain  reaches 


FIG.  127.  —  Side  View  of  Brain  and  Upper  Part  of  Spinal  Cord. 

B  =  bodies  of  vertebrae. 

C=  convolutions  of  the  right  cerebral  hemisphere. 
Cb  =  cerebellum. 
M.Ob  =  medulla  oblongata. 

N—  spinal  cord  with  s^pinal  nerves. 
Sp  =  spinous  process  of  vertebrae. 

downward  through  the  large  opening  (fo-ra'men  magnum)  at 
the  base  of  the  skull  and  becomes  continuous  with  the 
spinal  cord.  Since  the  two  portions  of  the  central  nervous 


A   STUDY   OF   THE   NERVOUS   SYSTEM  275 

system  last  mentioned  resemble  each  other  more  or  less  in 
their  structure,  we  will  consider  the  hindbrain  first. 

Hindbrain.  —  Examining  the  brain  from  the  side,  we  see 
that  the  relative  position  of  medulla  and  cerebellum  is  the 
same  as  in  the  frog's  brain.  The  human  medulla  looks  like 
an  enlarged  portion  of  the  spinal  cord,  and  this  was  also 
true  of  the  amphibian  brain.  The  first  striking  contrast  in 
the  appearance  of  the  two  brains  is  the  large  size  of  the 
human  cerebellum.  In  the  hindbrain  of  man,  too,  a  new 
structure  appears  in  the  shape  of  broad  bands  of  nerve 
tissue  that  pass  around  the  ventral  surface  of  the  medulla, 
connecting  the  two  halves  of  the  cerebellum.  It  is  called 
the  pons  Va-ro'li-i  (Latin  pons  =  bridge  +  Varolii  =  of  Varo- 
lius,  so  named  from  its  discoverer),  or  more  commonly  simply 
the  pons  (see  Figs.  128  and  130). 

Forebrain.  —  The  cerebral  hemispheres  of  the  forebrain 
are  enormously  developed;  indeed,  they  constitute  about 
three  fourths  of  the  human  brain.  They  fill  the  largest 
part  of  the  cranial  cavity,  completely  envelop  the  midbrain, 
and  partially  cover  the  hindbrain.  A  deep  fissure  sepa- 
rates the  two  hemispheres,  and  at  the  bottom  of  this  fissure 
a  broad  band  of  white  fibers  runs  across  like  a  bridge  from 
one  half  of  the  brain  to  the  other. 

The  surface  of  each  hemisphere  is  raised  in  ridges ;  these 
are  called  con-vo-lu'tions  (Latin  con-vol've-re  =  to  roll  up). 
The  various  convolutions  and  the  fissures  that  separate  them 
have  been  named  from  adjacent  bones  of  the  cranium  or  from 
the  investigators  who  have  studied  them.  The  most  promi- 
nent groove  is  the  fissure  of  SyVvi-us,  seen  at  the  side 
of  the  brain,  which  divides  the  upper  and  lower  portions 
of  the  cerebral  hemispheres.  The  fissure  of  Ro-lan'do 
divides  the  frontal  and  parietal  lobes.  Beneath  the  an- 
terior end  of  each  half  of  the  forebrain  is  a  small  olfactory 
lobe  (Fig.  128,  I). 

Midbrain.  —  Little  need  be  said  of  the  midbrain  of  man 
except  that  it  forms  an  isthmus  connecting  the  fore-  and 


276  STUDIES   IN  PHYSIOLOGY 

hindbrains.  The  relatively  small  optic  lobes  can  be  seen  by 
lifting  up  the  cerebral  hemispheres  from  the  cerebellum. 

Comparison  of  Human  and  Frog  Brains.  —  The  striking 
contrasts  Decween  these  two  brains  are  these:  First,  in 
the  human  brain  the  cerebral  hemispheres  and  cerebellum 
are  enormously  developed,  and  both  are  characterized  by 
the  presence  of  convolutions.  In  the  second  place,  while  the 
olfactory  and  optic  lobes  are  proportionately  large  in  the 
amphibian  brain,  in  man  they  are  relatively  small.  And 
finally,  the  two  brains  differ  widely  in  the  relation  to  each 
other  of  the  three  regions  '(fore-,  mid-,  and  hindbrains).  In 
the  frog's  brain  they  lie  in  a  straight  line,  one  in  front  of 
the  other;  the  axis  of  the  human  brain,  on  the  contrary, 
is  bent  in  three  places,  so  that  the  forebrain  extends  back 
and  covers  the  midbrain  and  hindbrain.  Both  in  man  and 
in  the  frog  the  central  nervous  system  is  hollow;  hence 
the  cavities  found  within  the  forebrain  are  continuous 
through  the  midbrain  and  hindbrain,  with  a  small  tube  that 
runs  within  the  spinal  cord. 

Section  of  Forebrain.  —  In  a  cross  section  of  the  cerebral 
hemispheres  one  finds  on  the  outside  a  covering  of  gray 
matter  known  as  the  cor'tex  (Latin  cortex  =  bark).  Since 
this  follows  all  the  elevations  and  depressions  on  the  surface 
of  th.0  brain,  it  is  clear  that  the  convolutions  largely  increase 
the  amount  of  gray  matter.  The  interior  mass  of  the  brain 
is  formed  of  white  matter,  in  which  are  several  important 
masses  of  gray  tissue  (ganglia).  In  the  cord,  as  we  have 
seen,  the  gray  .matter  is  found  in  the  central  regions;  in 
the  medulla  the  gray  and  white  matter  are  more  or  less 
intermingled ;  while  in  the  forebrain  most  of  the  gray  matter 
is  found  on  the  outside. 

Microscopic  Structure  of  the  Brain  —The  gray  matter  of 
the  brain,  like  that  of  the  spinal  cord,  consists  of  countless 
nerve  cells  of  various  shapes  and  sizes,  each  with  its 
several  rootlike  processes  and  its  single  axis  cylinder 
process.  Some  of  the  fibers  in  the  brain  connect  the  dif- 


A   STUDY   OF  THE  NERVOUS   SYSTEM  277 

ferent  parts  of  the  same  hemisphere ;  some  carry  messages 
from  one  hemisphere  to  the  other ;  others  bring  the  fore-, 
mid-,  and  hindbrains  into  connection  with  one  another  and 
with  the  spinal  cord ;  while  a  series  composed  of  still 


FIG.  128.  —The  Base  of  the  Brain. 

A  —  frontal  lobe  of  right  cerebral  hemisphere. 
B  =  temporal  lobe  of  right  cerebral  hemisphere. 
Cb  =  cerebellum. 

CC=  connection  between  two  hemispheres* 
M=  medulla  oblongata. 
I-XII—  cranial  nerves  (see  table  on  p.  279). 

others  conduct  messages  into  or  out  from  the  brain  along  the 
cranial  nerves.  In  passing  from  one  region  of  the  brain  to 
another,  a  nerve  impulse  may  run  through  a  dozen  or  more 
sets  of  cells  and  fibers.  Indeed,  the  most  intricate  systems 


278  STUDIES  IN  PHYSIOLOGY 

of  telegraph  wires  of  a  great  city  are  simplicity  itself  when 
compared  with  the  fibers  of  the  human  brain. 

Sensory  and  Motor  Cells  and  Fibers.  —  If  we  divide  the  cells 
of  the  gray  matter  according  to  their  functions,  we  shall  find 
at  least  two  distinct  classes.  At  the  end  of  the  afferent 
fibers  are  the  cells  of  the  first  class.  They  receive  the  mes- 
sages that  result  in  sensations,  and  are  therefore  called  sen- 
sory cells.  The  afferent  fibers,  too,  are  commonly  known  as 
sensory  nerves,  because  they  bring  in  -these  messages. 

In  the  second  class  are  the  cells  from  which  originate  the 
efferent  fibers.  The  function  of  these  cells  is  that  of  dis- 
patching the  messages  which  control  the  work  of  the  muscles 
and  other  organs.  To  these  cells  and  to  their  fibers  is 
therefore  given  the  name  motor. 

The  Cranial  Nerves.  —  Twelve  pairs  of  cranial  nerves  arise 
from  the  base  of  the  human  brain.  They  leave  the  cranium 
through  holes  in  the  base  of  the  skull,  and  are  distributed 
to  the  muscles,  skin,  and  sense  organs  of  the  head.  The  first 
ten  pairs  correspond  more  or  less  closely  to  the  ten  cranial 
nerves  of  the  frog;  true  eleventh  and  tivelfth  nerves  are 
wanting  in  the  amphibia.  In  the  table  on  the  following 
page  will  be  found  a  statement  of  the  origin,  distribution, 
and  function  of  each  of  these  twelve  pairs. 

7.   PHYSIOLOGY  OF  THE  BRAIN 

The  principal  functions  of  the  brain  may  for  convenience 
be  divided  into  (1)  reflex  activities,  (2)  conscious  activities, 
and  (3)  habits  or  automatic  activities. 

Reflex  Activities.  —  The  machinery  of  reflex  action  through 
the  spinal  cord  has  already  been  explained.  Similar  reflex 
processes  constitute  one  of  the  most  important  functions  of 
the  brain.  Suppose  I  inhale  some  pepper.  A  message  goes 
up  the  first  nerves  to  the  cells  in  my  brain.  This  mes- 
sage is  then  reflected  or  switched  off  to  cells  which  send 
impulses  down  the  nerves  which  control  the  muscles  of  my 


A  STUDY  OF  THE  NERVOUS  SYSTEM 


279 


THE  CRANIAL  NERVES 


NAME  OF 
NERVE 

KIND  OF 
NERVE 

CARRIES  MESSAGES 

FROM 

CARRIES  MESSAGES 

TO 

MESSAGES  KEBITLT 

IN 

First  pair 

afferent 

sense  organs  in 

olfactory  lobes, 

sensations    of 

(olfactory) 

(sensory) 

mucous  mem- 

thence to  sen- 

smell 

brane  of  nose 

sory  cells   of 

forebrain 

Second  pair 

afferent 

the  sensory  cells 

optic    lobes    of 

sensations   of 

(optic) 

(sensory) 

in  the  eyes 

midbrain, 

sight 

thence  to  sen- 

sory cells   of 

' 

forebrain 

efferent 

motor    cells  of 

muscles  that 

movements  of 

J-hird  pair   ] 
Fourth  pair  j 
Sixth  pair   ) 

(motor) 

forebrain,  out 
through  the 
medulla 

move  the  eyes 

the  eyes 

' 

afferent 

teeth  and  sense 

medulla,  thence 

sensations   of 

(sensory) 

organs  in 

to  sensory 

touch,  taste, 

tongue  and 

cells  of  fore- 

pain  (neural- 

Fifth pair 

and 

skin  of  head 

brain 

gia,      tooth- 
ache) 

efferent 

motor    cells   of 

muscles  of  jaws 

movements  of 

(motor) 

forebrain  out 

and  eyelids 

jaws  and  eye- 

thro' medulla 

lids 

Seventh  paii 

efferent 

motor    cells   of 

muscles  of  face 

changing     ex- 

(facial) 

(motor) 

forebrain   out 

and  scalp 

pressions    of 

thro'  medulla 

face         and 

speech 

Eighth  pair 

afferent 

sense  organs  of 

medulla,  thence 

sensations    of 

(auditory) 

(sensory) 

the  inner  ear 

to  sensory 

hearing   and 

cells  of  fore- 

balancing  of 

brain 

body 

f 

afferent 

sense  organs  of 

medulla,  thence 

sensations    of 

Ninth  pair 

(sensory) 

tongue  and 

to  sensory 

taste 

(glossoplmr-j 

and 

throat 

cells  of  fore- 

yngeal) 

efferent 

brain 

[ 

(motor) 

medulla 

muscles    of 

movements  of 

throat 

throat 

afferent 
(sensory) 

organs  of  diges- 
tion,   respira- 

medulla, thence 
to  sensory 

sensations     of 
hunger,  pain, 

Tenth  pair 

and 

tion,  and  cir- 
culation 

cells   of   fore- 
brain 

etc. 

(vagus) 

efferent 

motor   cells    of 

muscles   in   or- 

automatic   ac- 

(motor) 

medulla 

gans  of  diges- 

tion of  heart, 

tion,    respira- 

stomach, etc. 

I 

tion,  and  cir- 

Eleventh 

efferent 

motor    cells   of 

culation 

movements    of 

pair 

(motor) 

brain  out  thro' 

muscles  of 

muscles  of 

medulla 

shoulder 

shoulder,  etc. 

Twelfth  pair 

efferent 

motor    cells    of 

muscles  that 

movements  of 

(motor) 

forebrain   out 

move  the 

tongue  in 

thro'  medulla 

tongue 

speaking  and 

eating 

280  STUDIES  IN  PHYSIOLOGY 

chest.  I  then  sneeze,  and  thus  get  rid  of  the  pepper. 
Coughing,  winking,  blushing,  the  flow  of  saliva  at  the  sight 
of  savory  food  —  these  are  but  a  few  of  the  reflex  activities 
carried  on  by  the  brain. 

Conscious  Activities.  — As  long  as  we  keep  awake,  countless 
nerve  impulses  keep  pouring  into  our  brains.  When  the 
cells  of  the  gray  matter  receive  these  impressions,  we  usu- 
ally become  conscious  that  we  are  seeing,  smelling,  hearing, 
tasting,  or  feeling.  These  sensations  are  more  or  less  last- 
ing, too,  for  we  can  recall  distinctly  the  appearance  of  ob- 
jects that  we  saw  yesterday,  or  even  years  ago,  and  we  can 
hear  again,  as  it  were,  the  sounds  we  have  heard  in  the 
past.  In  some  unknown  way  these  impressions  are  stored 
away  in  the  protoplasm  of  our  brain,  and  constitute  our 
memory. 

Another  power  of  which  we  are  conscious  is  the  ability 
to  direct  the  movements  of  the  body.  I  can  rise  from  my 
seat,  walk  about,  talk,  or  change  the  expression  of  my  face 
as  I  will.  Or,  to  return  to  the  experience  of  burning  my 
finger,  I  might  by  the  exercise  of  my  will  power  prevent 
the  withdrawal  of  my  hand  from  the  hot  stove,  and  if  I 
had  enough  will  power  I  might  keep  it  there  until  it  was 
scorched. 

Localization  of  Functions  in  the  Brain.  —  The  facts  just 
stated  have  long  been  known,  but  only  in  recent  years 
have  we  discovered  that  certain  functions  are  located  in 
definite  parts  of  the  brain.  The  nerves  that  come  from 
the  eyes,  after  crossing  on  the  ventral  surface  of  the  brain, 
pass  through  the  midbrain,  and  finally  end  in  the  cells 
of  the  occipital  convolutions  of  the  forebrain.  Thus,  odd 
as  it  may  seem,  we  all  see  crosswise  and  in  the  back 
part  of  our  heads !  The  sense  of  hearing  is  located 
in  the  temporal  convolutions  below  the  fissure  of  Sylvius. 
Smell,  taste,  and  touch  have  not  as  yet  been  satisfactorily 
localized. 

In   the  convolutions    on   both   sides    of   the  -fissure   of 


A   STUDY  OF  THE   NERVOUS   SYSTEM 


281 


Rolando  are  the  nerve  cells  that  control  the  movements 
of  the  arms  and  legs.  If  the  right  half  of  the  brain  in 
this  region  be  injured,  paralysis  on  the  left  side  of  the 
body  is  likely  to  follow.  From  facts  like  these  we  know 
that  the  nerve  trunks,  after  leaving  the  motor  cells,  cross 
the  brain  and 
spinal  cord,  and 
supply  the  op- 
posite side  of  the 
body.  This  is 
true  of  nearly  all 
the  nerve  trunks. 
A  right-handed 
man  is  there- 
fore left-brained. 
One  should,  how- 
ever,  guard 
against  the  idea 
that  the  brain 
can  be  divided 
into  different  re-  FlG'  129'~side  View  of  Brain,  showing  Localiza- 
tion of  Functions, 
gions  that  work 

independently.  An  injury  to  a  single  region  of  the  brain 
often  destroys,  for  a  time  at  least,  all  consciousness  and 
all  power  of  motion.  This  is  often  the  result  of  a  blow 
on  the  head. 

Habitual  Activities —  Can  you  remember  the  time  when 
you  learned  to  write?  If  so,  you  will  recall  that  each 
letter  was  traced  laboriously  by  a  conscious  effort  of  your 
brain  to  guide  the  muscles  of  your  fingers.  Writing,  in 
our  early  years,  belonged  to  the  group  of  our  conscious 
activities.  But  as  time  went  on,  less  and  less  of  our 
attention  was  needed  for  this  mechanical  process,  until 
now  our  fingers  seem  to  move  of  themselves.  Walking, 
bicycle  riding,  swimming,  playing  the  piano,  putting  on 
our  clothes,  conveying  the  food  to  our  mouths  —  none  of 


282  STUDIES  IN  PHYSIOLOGY 

these  activities  require  our  attention.  We  have  made  these 
movements  so  many  times  that  they  have  become  automatic. 
In  other  words  the  conscious  parts  of  our  brains,  our 
cerebral  hemispheres,  have  trained  the  lower  nerve  centers 
(central  ganglia,  medulla,  and  cerebellum)  to  direct  a  good 
many  of  our  everyday  doings.  Our  attention  is  thus  set 
free  to  carry  on  other  kinds  of  work. 

"  As  every  one  knows,  it  takes  a  soldier  a  long  time  to 
learn  his  drill  —  for  instance,  to  put  himself  into  the  atti- 
tude of  ' attention7  at  the  instant  the  word  of  command 
is  heard.  .  But,  after  a  time,  the  sound  of  the  word  gives 
rise  to  the  act,  whether  the  soldier  be  thinking  of  it,  or 
not.  There  is  a  story,  which  is  credible  enough  though 
it  may  not  be  true,  of  a  practical  joker,  who,  seeing  a  dis- 
charged veteran  carrying  home  his  dinner,  suddenly  called 
out  ' Attention!'  whereupon  the  man  instantly  brought  his 
hands  down,  and  lost  his  mutton  and  potatoes  in  the  gutter. 
The  drill  had  been  thorough,  and  its  effect  had  become 
embodied  in  the  man's  nervous  structure." — Huxley's  "  Les- 
sons in  Elementary  Physiology,"  Macmillan  Company. 

Importance  of  Habit.  —  The  tremendous  importance  of 
making  our  habits  our  allies  instead  of  our  enemies  can- 
not be  emphasized  too  strongly. 

"  The  hell  to  be  endured  hereafter,"  says  Professor  James, 
"of  which  theology  tells,  is  no  worse  than  the  hell  we 
make  for  ourselves  in  this  world  by  habitually  fashioning 
our  characters  in  the  wrong  way.  Could  the  young  but 
realize  how  soon  they  will  become  mere  walking  bundles 
of  habits,  they  would  give  more  heed  to  their  conduct 
while  in  the  plastic  state.  We  are  spinning  our  own  fates, 
good  or  evil,  and  never  to  be  undone.  Every  smallest 
stroke  of  virtue  or  of  vice  leaves  its  never-so-little  scar. 
The  drunken  Eip  Van  Winkle,  in  Jefferson's  play,  excuses 
himself  for  every  fresh  dereliction  by  saying,  'I  won't 
count  this  time!'  Well!  he  may  not  count  it,  and  a  kind 
Heaven  may  not  count  it;  but  it  is  being  counted  none 


A   STUDY  OF  THE   NERVOUS   SYSTEM  283 

the  less.  Down  among  his  nerve  cells  and  fibers  the  mole- 
cules are  counting  it,  registering  and  storing  it  up  to  be 
used  against  him  when  the  next  temptation  comes.  Noth- 
ing we  ever  do  is,  in  strict  scientific  literalness,  wiped  out. 
Of  course  this  has  its  good  side  as  well  as  its  bad  one. 
As  we  become  permanent  drunkards  by  so  many  separate 
drinks,  so  we  become  saints  in  the  moral,  and  authorities 
in  the  practical  and  scientific  spheres,  by  so  many  sepa- 
rate acts  and  hours  of  work.  Let  no  youth  have  any 
anxiety  about  the  upshot  of  his  education,  whatever  the 
line  of  it  may  be.  If  he  keep  faithfully  busy  each  hour 
of  the  working  day,  he  may  safely  leave  the  final  result 
to  itself.  He  can  with  perfect  certainty  count  on  waking 
up  some  fine  morning,  to  find  himself  one  of  the  compe- 
tent ones  of  his  generation,  in  whatever  pursuit  he  may 
have  singled  out.'71 

8.   HYGIENE  OF  THE  NERVOUS  SYSTEM 

Changes  in  the  Nervous  System  during  Life.  —  The  nervous 
system  of  a  child  at  birth  differs  in  many  ways  from  that 
of  an  adult.  In  the  first  place  the  nerve  cells  in  the  cortex, 
when  first  formed,  are  more  or  less  spherical  in  shape. 
During  development,  however,  the  axis  cylinder  and  the 
various  branching  processes  grow  out  through  the  tissues 
from  the  body  of  each  cell  something  as  roots  work  their 
way  through  the  soil.  In  this  way  different  nerve  cells 
are  brought  into  relation  with  each  other  and  with  different 
parts  of  the  body.  Again,  when  first  formed,  axis  cylin- 
ders are  naked  and  they  only  gradually  become  covered 
with  a  medullary  sheath.  The  central  nervous  system  also, 
like  other  parts  of  the  body,  increases  greatly  in  size,  es- 
pecially -during  the  early  years  of  life.  Both  growth  and 
development^  however,  are  slow,  and  hence  only  by  degrees 
do  we  get  control  over  the  various  organs  of  the  body. 

1  Professor  James,  "  Psychology."     Henry  Holt  &  Co. 


284  STUDIES  IN  PHYSIOLOGY 

Throughout  life,  too,  continual  use  of  the  nerve  cells  in- 
volves a  destructive  metabolism  of  their  protoplasm.  This 
wasting  process  must,  therefore,  be  succeeded  by  repair. 

Necessary  Conditions  for  a  Healthy  Nervous  System.  —  In 
studying  the  hygiene  of  the  muscles  we  found  that  four 
conditions  were  necessary  for  healthy  muscular  activity  (see 
p.  202).  That  the  nervous  system,  too,  may  develop  as  it 
should  and  that  it  may  do  its  work  properly,  the  same  four 
conditions  are  essential;  namely,  food,  fresh  air,  various 
kinds  of  activity,  and  periods  of  rest. 

Food  and  Air.  —  It  is  estimated  that  in  the  nervous  system 
of  an  adult  human  being  there  are  at  least  three  thousand 
millions  (3,000,000,000)  of  nerve  cells.  Each  of  these  cells 
must  be  supplied  with  nutritious  food  and  pure  air,  or  it 
becomes  stunted  in  its  growth  and  unable  to  do  its  proper 
work.  These  busy  cells  are  constantly  giving  off  carbon 
dioxid,  water,  and  other  wastes,  and  if  these  are  not  re- 
moved and  fresh  oxygen  supplied,  one  feels  (as  we  have 
learned  on  p.  226)  a  drowsiness  and  headache,  and  is  unable 
to  think  clearly.  Well-ventilated  rooms,  both  by  day  and 
by  night,  are  of  prime  importance  in  the  hygiene  of  the 
nervous  system. 

Varied  Activity.  —  Fortunately  for  the  well-being  of  the 
race,  genius  is  rare,  for  genius  is  usually  a  kind  of  one- 
sided mental  life.  To  develop  a  well-balanced  brain  one 
must  be  active  along  many  lines.  Experience  tells  us,  too, 
that  we  cannot  work  successfully  at  the  same  task  hour 
after  hour  without  some  change.  Hence,  varied  activity  is 
an  important  principle  in  sound  education.  The  young 
child  must,  of  necessity,  turn,  after  a  short  time,  from  one 
lesson  to  another,  and  all  lessons  must  at  length  give  way 
to  the  relaxation  of  play.  In  planning  the  school  curricu- 
lum we  seek  to  develop  the  sensory  areas  of  the  child's 
brain  by  nature  study  and  science;  the  motor  cells  are 
trained  by  manual  training  and  physical  exercise.  Unfor- 
tunate is  the  boy  who  fails  to  find  exhilaration  in  baseball, 


A   STUDY   OF  THE  NERVOUS   SYSTEM  285 

bicycle  riding,  or  general  athletics,  for  these  sports,  when 
properly  regulated,  besides  developing  strong  lungs  and 
vigorous  muscles,  are  important  means  of  educating  the 
nerve  cells  and  fibers. 

Not  only  in  youth,  but  throughout  life,  must  the  student, 
the  business  man,  or  the  laborer,  at  the  end  of  a  day's 
employment,  find  relaxation  in  other  forms  of  activity.  If 
he  fails  to  do  this,  not  only  will  he  become  weary  of  his 
work,  but  also  he  will  finally  come  to  lose  the  power  of 
enjoying  the  pleasures  he  has  been  neglecting.  In  the 
later  years  of  his  life,  the  great  naturalist,  Charles  Darwin, 
wrote  as  follows :  "  My  mind  seems  to  have  become  a  kind 
of  machine  for  grinding  general  laws  out  of  large  collections 
of  facts.  ...  If  I  were  to  live  my  life  again,  I  would 
have  made  a  rule  to  read  some  poetry  and  listen  to  some 
music  at  least  once  every  week;  for  perhaps  the  parts  of 
my  brain  now  atrophied  would  thus  have  been  kept  alive 
through  use.  The  loss  of  these  tastes  is  a  loss  of  happiness, 
and  may  possibly  be  injurious  to  the  intellect,  and  more 
probably  to  the  moral  character,  by  enfeebling  the  emo- 
tional part  of  our  nature." 

Rest.  —  Experiments  with  animals  show  a  striking  dif- 
ference in  the  appearance  of  nerve  cells  before  and  after 
vigorous  exercise.  In  the  nerve  cells  of  a  bird  that  has 
been  flying  all  day,  the  protoplasm  has  a  distinctly  granular 
appearance,  which  is  not  seen  in  a  specimen  killed  before 
exercise.  The  tired  nerve  cells  can  be  restored  by  rest 
alone.  Experience,  too,  tells  us  that  sleep  is  the  best 
remedy  for  most  of  our  ills.  In  childhood  and  youth  an 
abundance  of  sleep  is  absolutely  essential  for  healthy  de- 
velopment. Late  hours  of  evening  entertainment  or  of  study 
must  never  be  alloived  to  keep  growing  boys  or  girls  from  having 
at  least  nine  hours  of  dreamless  sleep. 

Effect  of  Alcohol  on  the  Nervous  System.  —  "  The  effect  of 
alcohol  appears  to  be,  as  it  were,  to  shave  off  the  nervous 
system,  layer  by  layer,  attacking  first  the  highest-developed 


286  STUDIES  IN  PHYSIOLOGY 

faculties  and  leaving  the  lowest  to  the  last,  so  that  we  find 
that  a  man's  judgment  may  be  lessened,  though  at  the  same 
time  some  lower  faculties,  such  as  the  imagination  and 
emotions,  may  appear  to  be  more  active  than  before.  .  .  . 
Thus  you  find  that  after  a  man  has  taken  alcohol  his  judg- 
ment may  be  diminished,  but  he  may  become  more  loqua- 
cious and  more  jolly  than  before.  Then  after  a  while  his 
faculties  become  dull ;  he  gets  stupid  and  drowsy.  .  .  . 
Later  on  it  affects  the  motor  centers,  probably  the  cere- 
bellum, so  that  the  man  is  no  longer  able  to  walk,  and  reels 
whenever  he  makes  the  attempt.  At  this  time,  however, 
he  may  still  be  able  to  ride  (on  horseback),  and  a  man  who 
is  so  drunk  that  he  cannot  walk  and  cannot  speak  may  ride 
perfectly  well.  .  .  .  Later  on  the  further  anaesthetic  action 
of  the  alcohol  abolishes  sensation,  and  its  paralyzing  action 
destroys  the  power  of  the  spinal  cord,  so  that  the  man  is 
no  longer  able  even  to  ride ;  but  still  the  respiratory  center 
in  the  medulla  will  go  on  acting,  and  it  is  not  until  enor- 
mous doses  of  alcohol  have  been  given  that  respiration 
becomes  paralyzed. 

"Alcohol  .  .  .  makes  all  the  nervous  processes  slower, 
but  at  the  same  time  it  has  the  curious  effect  of  producing 
a  kind  of  mental  anaesthesia,  ...  so  that  these  processes 
seem  to  the  person  himself  to  be  all  quicker  than  usual, 
instead  of  being,  as  they  really  are,  much  slower.  Thus  a- 
man,  while  doing  things  much  more  slowly  than  before,  is 
under  the  impression  that  he  is  doing  things  very  much 
more  quickly.  What  applies  to  these  very  simple  processes 
applies  also  to  the  higher  processes  of  the  mind;  and  a 
celebrated  author  once  told  me  that  if  he  wrote  under  the 
influence  of  a  small  quantity  of  alcohol,  he  seemed  to,  him- 
self to  write  very  fluently  and  to  write  very  well,  but  when 
he  came  to  examine  what  he  had  written  next  day,  after 
the  effect  of  the  alcohol  had  passed  off,  he  found  that  it 
would  not  stand  criticism." — T.  LAUDER  BRUNTON,  London, 
"  Lectures  on  the  Action  of  Medicine/7  pp.  190,  191,  194. 


A  STUDY  OF  THE  NERVOUS  SYSTEM  287 

9.   A  COMPARATIVE  STUDY  OF  THE  NERVOUS  SYSTEM 

Nerve  Functions  in  Amoeba.  —  It  is,  of  course,  impossible 
to  speak  of  anything  like  a  nervous  system  in  single-celled 
animals.  We  found,  however,  that  the  amoeba  could  move 
without  any  appendages,  could  take  in  food  without  any 
mouth,  and  could  carry  on  the  processes  of  digestion,  respira- 
tion, and  excretion  without  any  stomach,  lungs,  or  kidneys. 
So,  too,  this  bit  of  protoplasm,  although  it  is  without  a 
nervous  system,  has  what  we  may  at  least  call  nervous 
irritability.  If  the  slide  over  which  an  amoeba  is  crawling 
be  suddenly  jarred,  the  animal  will  pull  in  its  false  feet 
and  assume  a  spherical  form.  It  can  distinguish  particles 
of  food  from  bits  of  sand,  for  it  will  surround  the  former 
with  its  body  protoplasm ;  dirt  particles,  on  the  other  hand, 
are  passed  by.  The  amoeba  is  also  affected  by  different 
colors  of  light.  It  moves  about  most  vigorously  when  yellow 
ra}rs  are  thrown  upon  it ;  in  the  presence  of  violet  light  it 
remains  quiet.  All  these  facts  prove  conclusively  that 
the  amoeba  possesses  something  at  least  akin  to  nervous 
functions. 

The  Nervous  System  of  the  Earthworm The  "  brain  "  of 

the  earthworm  consists  of  two  small  pear-shaped  ganglia 
placed  end  to  end  across  the  dorsal  surface  of  the  esophagus 
(see  Fig.  38).  Several  nerves  connect  this  part  of  the  nerv- 
ous system  with  the  sense  organs  on  the  anterior  end  of  the 
body.  From  each  of  the  brain  ganglia  we  have  mentioned,  a 
nerve  trunk  runs  around  to  the  ventral  surface  of  the  esoph- 
agus. There  the  two  meet  and  run  as  a  double  chain  to 
the  posterior  end  of  the  body.  In  each  segment  this  nerve 
chain  has  an  enlargement  or  ganglion  (each  of  which  really 
consists  of  two  parts).  Nerves  are  given  off  in  pairs  along 
the  side  of  this  chain  of  ganglia,  and  connect  this  central 
nervous  system  with  the  sense  organs  on  the  surface  of  the 
body  and  with  the  muscles. 

Nervous  Functions  in  the  Earthworm.  —  Earthworms  rarely 


288  STUDIES  IN  PHYSIOLOGY 

come  out  of  their  burrows  except  at  night,  hence,  although 
they  have  no  eyes,  they  can  distinguish  light  from  dark- 
ness. These  animals  take  in  certain  substances  for  food 
and  refuse  to  take  others,  which  indicates  that  they  can 
taste  or  smell,  or  both.  The  contraction  of  the  various 
muscles  in  the  body  wall,  the  movement  of  the  bristles,  the 
rhythmic  pulsations  of  the  blood  vessels,  and  the  action  of 
the  various  glands,  are  all  controlled  by  the  nervous  system. 
We  know,  too,  that  when  an  earthworm  is  cut  in  two,  both 
pieces  can  move  about  for  a  time.  Hence  the  ganglia  in  dif- 
ferent parts  of  the  body  can  act  more  or  less  independently. 
The  posterior  region,  however,  soon  dies.  But  the  anterior 
part,  which  has  the  brain,  can  often  develop  new  segments 
and  in  time  become  a  complete  worm. 

The  Nervous  System  of  Invertebrates  and  of  Vertebrates.  — 
In  the  earthworm,  as  we  have  just  seen,  the  central  nervous 
system  is  situated  in  the  ventral  region  of  the  body.  The 
same  is  true  in  starfishes,  clams,  lobsters,  and  insects.  In- 
deed, in  all  invertebrates  we  find  most  of  the  ganglia  (when 
they  are  present  at  all)  to  be  ventral.  Vertebrates,  on  the 
other  hand,  have  a  dorsal  brain  and  spinal  cord  wholly  or 
largely  inclosed  within  a  skull  and  spinal  column,  and  most 
vertebrates,  too,  have  two  chains  of  sympathetic  ganglia 
which  extend  along  the  dorsal  region  of  the  body  cavity  on 
each  side  of  the  spinal  column,  and  which  largely  control 
the  organs  of  digestion,  circulation,  and  excretion.  But  while 
the  general  plan  of  the  nervous  system  in  all  vertebrates 
is  the  same,  striking  differences  occur  in  detail.  This  will 
be  clearly  shown  by  — 

A  Comparison  of  Vertebrate  Brains.  —  On  p.  289  are  repre- 
sented the  brains  of  the  salmon  (fish),  the  frog  (amphibian), 
the  alligator  (reptile),  the  pigeon  (bird),  and  the  dog  and 
man  (mammals).  Thus  we  have  a  representative  form  of 
each  of  the  five  groups  of  vertebrates,  and  for  convenience 
in  comparison  the  brains,  in  spite  of  their  great  differences 
in  actual  volume,  are  represented  as  though  they  were  of  the 


A  STUDY  OF  THE  NERVOUS  SYSTEM  289 


Brain  of  Salmon. 


Brain  of  Frog. 


Brain  of  Alligator. 


Brain  of  Pigeon. 


Lai 


Brain  of  Dog. 


KO. 
Brain  of  Man. 


FIG.  130.  —  A  Comparison  of  Brains  (all  represented  as  though  they  were 
of  the  same  size).    Left  side  view  (except  alligator's  brain). 


HH=  cerebellum. 

L.ol  =  olfactory  lobe. 

Med  =  spinal  cord. 

MH=  midbrain  (optic  lobes). 

NH=  medulla. 


Po  =  pons. 
VH=  forebrain. 
I-XII  =  cranial  nerves. 
1,  2  =  spinal  nerves. 


same  size.     The  following  striking  differences  are  seen  as 
one  follows  the  series  from  the  fish  to  man :  — 

(1)  There  is  a  gradual  increase  in  the  size  of  the  cerebral 
hemispheres,  until  in  man  they  constitute  three  fourths  of 
the  whole  brain.  The  surface  of  the  hemispheres  in  all  the 
lower  forms  is  smooth,  and  hence  the  cortex  is  usually  small 


290  STUDIES  IN  PHYSIOLOGY 

in  extent.  In  the  higher  mammals,  on  the  other  hand,  the 
convolutions  increase  enormously  the  gray  matter  on  the 
surface  of  the  brain,  and  this  accounts  in  a  large  measure 
for  the  fact  that  man  is  the  highest  type  of  animal  life. 

(2)  While  the  relative  size  and  importance  of  the  cerebral 
hemispheres  of  the  forebrain  increase  as  one  ascends  the 
series  from  fish  to  man,  one  notes  a  more  or  less  propor- 
tional decrease  in  the  size  of  the  olfactory  lobes.     In  man 
the  olfactory  lobes  are  very  small.     Other  mammals,  like  the 
dog,  in  which  the  sense  of  smell  is  keen,  have  somewhat 
larger  olfactory  lobes. 

(3)  The  increase  in  size  and  complexity  of  the  midbrain 
and  the  hindbrain  is  not  as  striking  as  is  that  of  the  fore- 
brain.     Yet  when  one  compares  the  structure  and  functions 
of  the  optic  lobes,  the  cerebellum,  and  the  medulla  of  man 
with  these  parts  of  the  brain  of  any  of  the  lower  groups  of 
animals,  one  sees  that  these  parts,  too,  develop  enormously 
as  one  follows  up  the  animal  series.     Doubtless  one  of  the 
surest  ways  of  determining  whether  an  animal  stands  high 
or  low  in  the  scale  of  life  is  by  making  a  careful  study  of 
the  degree  of  complexity  of  its  nervous  system. 


CHAPTER   XIV 


A  STUDY  OF  THE  SENSES 
1.   THE  SENSE  OP  TOUCH 

The  Sense  Organs  of  Touch.  —  In  our  study  of  the  skin  we 
found  that  small  hillocks  or  papillae  of  the  dermis  project 
outward  into  the  epidermis,  and 
that  within  many  of  these 
papillae  are  the  terminations  of 
afferent  (sensory)  nerve  fibers. 
In  some  cases  these  terminals 
take  the  form  of  minute  swell- 
ings on  the  nerve  fibers;  in 
other  papillae  there  are  more  or 
less  complicated  tactile  corpus- 
cles, each  composed  of  sensory 
cells  and  a  tangle  of  sensory 
fibers.  In  many  regions,  also, 
of  the  skin  branching  nerve 
fibers  pass  out  and  end  in  little 
knobs  between  the  lower  cells 
of  the  epidermis.  From  these 
terminations,  whatever  their 
form  or  position,  nerve  fibers 
extend  to  the  central  nervous 
system,  and  so,  by  a  relay  sys- 
tem of  fibers,  the  external  regions  of  the  body  are  brought 
into  communication  with  the  sensory  cells  of  the  spinal 
cord  and  the  brain., 

291 


FIG.  131.  — A  Tactile  Corpuscle 
in  a  Papilla  of  the  Dermis. 

a  =  knobs  on  the  branches  of  a 

nerve  in  the  papilla. 
n  =  nerve  fiber  ending  in  papilla. 


292  STUDIES   IN  PHYSIOLOGY 

Sensations  of  Touch.  —  If  I  rub  a  piece  of  cloth  over  the 
tip  of  my  finger,  I  can  determine,  even  with  my  eyes  closed, 
whether  the  cloth  is  smooth  or  rough.  Its  characteristics 
could  be  determined  even  more  accurately  by  rubbing  it 
on  the  lips  or  forehead.  But  if  I  were  to  apply  the  piece 
to  the  back  of  my  neck,  I  should  find  the  latter  to  be  far 
less  sensitive  than  are  the  lips  and  finger  tips.  The  degree 
of  sensitiveness  of  the  various  parts  of  the  body  can  be 
determined  very  accurately  in  the  following  way.  When  I 
separate  the  points  of  a  pair  of  scissors  about  three  inches, 
and,  with  my  eyes  closed,  apply  the  two  points  to  the  back 
of  my  neck,  I  can  get  a  distinct  impression  of  each.  When, 
however,  the  points  are  brought  within  two  inches  of  each 
other,  they  give  the  sensation  of  a  single  point.  If  the 
points  are  applied  to  the  lips,  they  can  be  distinguished  as 
two,  even  when  within  about  one  sixth  inch,  and  on  the  tip 
of  the  tongue  the  points  need  be  separated  but  one  twenty- 
fourth  of  an  inch. 

It  is  interesting  in  this  connection  to  note  that  the  degree 
of  sensitiveness  of  a  given  part  can  be  increased  by  train- 
ing. For  instance,  one  experimenter  found  that  on  a  certain 
portion  of  his  arm,  at  the  end  of  a  week  of  training,  he 
could  distinguish  the  points  as  two  when  they  were  sepa- 
rated about  three  quarters  of  an  inch;  at  the  end  of  the 
fourth  week  of  training,  they  could  be  felt  as  two  even  when 
only  one  sixth  of  an  inch  apart.  In  other  words,  he  had 
by  training  his  brain  increased  the  sensitiveness  of  the  area 
experimented  upon  more  than  four  times. 

The  following  simple  experiment  shows  how  easy  it  is  for 
one  to  be  mistaken  in  regard  to  the  judgment  of  one's  sense 
impressions.  If  I  close  my  eyes,  cross  my  middle  and  fore- 
finger, and  then  place  between  the  two  finger  tips  a  small 
marble  or  pea,  I  seem  to  be  touching  two  distinct  objects. 
This  is  due  to  the  fact  that  under  ordinary  conditions  it  is 
impossible  to  touch  an  object  at  the  same  time  with  the 
thumb  side  of  the  forefinger  and  with  the  little  finger  side 


A   STUDY   OF  THE   SENSES  293 

of  the  middle  finger.  Hence,  with  my  eyes  closed,  I  seem 
to  forget  that  my  fingers  are  crossed,  and  so  draw  the  wrong 
conclusion  that  the  two  impressions  are  caused  by  two  dis- 
tinct objects. 

2.   GENERAL  SENSES 

Sensations  of  Temperature.  —  Besides  the  sensations  of  touch 
which  we  have  just  described,  the  skin  has  the  power  of. 
noting  differences  in  the  temperature  of  surrounding  objects. 
If  I  put  my  right  hand  into  cold  water  and  my  left  into  hot 
water,  and  then  plunge  both  hands  into  a  dish  of  lukewarm 
water,  the  latter  will  seem  warm  to  my  right  hand  and  cold 
to  my  left.  These  temperature  sensations  may  likewise  be 
due  to  changes  in  the  internal  condition  of  my  body.  Thus, 
if  I  have  been  exercising  vigorously  on  a  windy  day  and 
then  come  into  a  room  the  temperature  of  which  is  70°,  I 
feel  uncomfortably  warm.  Blood  is  flowing  in  large  quan- 
tity through  my  skin,  my  temperature  terminations  send  im- 
pulses to  my  brain,  and  I  infer  that  the  room  is  warm.  If 
I  act  upon  impulse,  I  open  a  window  and  sit  in  a  draught. 
Whereas,  if  I  should  keep  still  until  my  circulation  had 
returned  to  its  normal  condition,  I  should  soon  feel  comfort- 
able without  taking  any  risk  of  catching  cold.  Since  the 
temperature  sense  is  very  delicate  in  the  cheeks  and  fore- 
head, where  the  sense  of  touch  is  not  well  developed,  many 
physiologists  conclude  that  the  nervous  apparatus  is  a  dif- 
ferent one  for  the  senses  of  touch  and  temperature. 

Sensations  of  Pain.  —  When  I  put  my  finger  on  a  hot  stove, 
I  cease  to  get  an  impression  of  temperature,  but  feel  rather 
a  sense  of  pain.  The  same  is  true  if  an  object  presses 
heavily  upon  any  part  of  the  skin.  In  health  we  are  en- 
tirely unconscious  of  the  presence  of  the  organs  of  digestion, 
circulation,  or  respiration.  But  let  any  one  of  these  in- 
ternal organs  become  deranged,  and  we  become  conscious  of 
this  fact  by  sensations  of  pain.  Hence  we  infer  that  cer- 
tain nerves  are  specially  adapted  to  carry  to  the  central 


294  STUDIES  IN  PHYSIOLOGY 

nervous  system  impulses  that  result  in  sensations  of  pain. 
We  should  regard  painful  sensations,  like  danger  signals, 
as  of  use  to  us  in  preventing  permanent  injury  to  the  body. 
Sensations  of  Hunger  and  Thirst.  —  If  food  is  withheld  from 
our  bodies  for  a  time,  we  become  conscious  of  a  sensation  of 
hunger.  We  can  get  rid  of  this  feeling,  temporarily  at  least, 
by  swallowing  pebbles  or  any  other  indigestible  substances. 
We  therefore  infer  that  hunger  in  its  early  stages  is  largely 
due  to  the  condition  of  the  mucous  membrane  of  the 
stomach.  But,  since  hunger  likewise  disappears  if  food 
is  injected  directly  into  the  blood,  we  conclude  that  this  is 
a  general  sensation  belonging  to  the  whole  body.  Thirst, 
too,  while  it  can  be  relieved  for  a  time  by  moistening  the 
mucous  membrane  of  the  throat,  soon  reappears  unless  water 
is  swallowed  and  absorbed  by  the  blood,  or  unless  water  is 
injected  directly  into  the  blood  vessels.  Hence  we  conclude 
that  sensations  of  hunger  and  thirst,  and  the  feeling  of  satis- 
faction that  follows  the  taking  of  food,  are  common  sensations 
which  acquaint  us  with  the  general  condition  of  the  whole  body, 
and  especially  of  the  blood. 

3.   THE  SENSE  OF  TASTE 

Papillae  of  the  Tongue.  —  While  studying  the  tongue,  we 
called  attention  to  certain  elevations  called  papillae.  These 
differ  from  those  of  the  dermis  in  the  fact  that  the  mucous 
membrane  follows  the  outline  of  the  papillae  on  the  tongue, 
and  so  the  latter  project  from  the  surface.  On  the  tongue 
there  are  three  kinds  of  papillae.  The  Jil'i-form  (Latin 
filum  =  a  thread)  are  long  and  slender,  and  are  found  in 
great  numbers  along  the  sides  and  at  the  tip  of  the  tongue. 
These  regions  we  found  (p.  292)  to  be  most  sensitive  to  tac- 
tile impressions,  and  so  we  believe  that  the  filiform  papillae 
send  to  the  brain  impulses  that  result  in  sensations  of  touch. 

A  second  class  of  papillae  are  the  fun'gi-form  (Latin  fun- 
gus =  a  mushroom).  In  shape  they  resemble  a  mushroom 


A  STUDY  OF  THE   SENSES  295 

or  toadstool.  They  are  less  numerous  than  the  filiform 
papillae,  but  can  be  easily  recognized  on  the  sides  and  top 
of  one's  tongue  as  rounded  elevations  of  a  deep  red  color 
(see  Fig.  27).  Near  the  back  of  the  tongue  are  eight  to  twelve 
papillae  of  large  size.  Each  is  situated  in  a  cup-shaped  depres- 
sion, and  hence  is  surrounded  by  a  ditch,  outside  of  which  is 
a  wall  of  mucous  membrane.  From  this  fact  these  large  ele- 
vations are  known  as  cir-cum-val'late  papillce,  (Latin  circum- 
vallare  =  to  surround  with  a  wall). 


B      \      * 
C 

FIG.  132.  —  Diagram  of  a  Circumvallate  Papilla,  and  of  Taste  Buds. 

A  =  section  of  a  circumvallate  e  =  epidermis. 

papilla.  m  =  projecting  hair. 

B  =  two  taste  buds.  n  =  four  inner  cells  of  bud. 

c  =  outer  or  protective  cells.  t  =  taste  buds. 

d  =  dermis.  x  =  nerve  fibers. 

The  Taste  Buds.  —  In  the  mucous  membrane  which  covers 
the  fungiform  and  circumvallate  papillae  are  little  groups 
of  cells  arranged  in  layers  something  like  the  leaves  in  a 
bud.  The  outer  cells  of  each  taste  bud  form  a  protective 
covering  for  the  inner  taste  cells.  The  latter  are  spindle- 
shaped  ;  their  outer  ends  project  from  the  taste  bud  as  hair- 
like  processes,  while  the  inner  portion  of  each  is  connected 
with  fine  branches  of  the  fifth  or  ninth  pairs  of  cranial  nerves. 
Taste  buds  like  those  on  the  papillae  are  also  scattered  here 
and  there  over  the  surface  of  the  tongue  and  the  palate. 

Sensations  of  Taste.  —  If  I  close  my  eyes  and  tightly  hold 


296  STUDIES  IN  PHYSIOLOGY 

my  nose,  and  then  put  into  my  mouth  successively  a  piece 
of  potato,  a  piece  of  apple,  and  a  piece  of  onion,  I  am  unable 
to  distinguish  one  from  another.  In  other  words,  we  learn 
that  many  of  our  foods  are  not  tasted,  but  smelled.  The 
same  fact  is  demonstrated  by  an  experience  with  a  head 
cold,  when  the  mucous  membrane  of  the  throat  and  nose 
cavities  is  so  inflamed  that  the  odorous  particles  do  not 
affect  the  sense  organs  of  smell;  we  then  lose  the  power 
of  "tasting"  our  food. 

In  reality,  we  can  taste  but  four  different  classes  of  sub- 
stances, namely,  sweet,  sour,  bitter,  and  salt.  All  the  vari- 
ous "  flavors  "  of  foods  and  drinks  are  therefore  distinguished 
by  smell,  and  not  by  taste.  By  the  help  of  the  taste  buds 
alone  we  cannot  even  distinguish  the  sour  of  vinegar  from 
that  of  hydrochloric  acid.  Before  we  can  taste  any  sub- 
stance, however,  it  must  be  made  into  a  solution,  otherwise 
the  sensory  hairs  of  the  taste  buds  are  not  affected.  This 
is  the  reason  why  sand  and  other  insoluble  substances  are 
tasteless. 

4.   THE  SENSE  OF  SMELL 

The  Nasal  Cavities.  —  The  two  nose  cavities  are  separated 
by  a  central  partition  composed  partly  of  bone  and  partly 
of  cartilage.  These  cavities  communicate  with  the  outside 
air  by  the  two  external  nostrils,  and  at  the  back  they  open 
by  the  internal  nostrils  into  the  throat  cavity.  Each  nasal 
cavity  is  separated  from  the  cavity  of  the  mouth  by  the  hard 
palate,  and  from  the  brain  by  a  portion  of  the  ethmoid  bone. 
In  the  latter  are  numerous  perforations  through  which  pass 
the  branches  of  the  first  pair  of  olfactory  nerves.  Hence 
this  roof  of  the  nasal  cavities  is  known  as  the  crib'i-form 
plate  (Latin  cribrum  =  a  sieve).  Projecting  from  the  outer 
wall  of  each  nasal  cavity,  as  we  learned  in  studying  the 
skeleton,  are  three  thin  bones,  each  rolled  more  or  less  like 
a  scroll ;  they  are  the  superior,  middle,  and  inferior  spongy 
or  turbinate  bones. 


A   STUDY   OF   THE   SENSES 


297 


The  Sense  Organs  of  Smell.  —  The  whole  interior  of  the 
nose  is  lined  with  mucous  membrane.  This  membrane, 
however,  differs  greatly  in  its 
structure  in  the  upper  or  ol- 
factory region  of  each  cavity 
and  in  the  lower  or  respiratory 
region.  In  the  latter  one  finds 
ciliated  cells  much  like  those 
which  line  the  air  passages 
from  the  throat  to  the  lungs. 
In  the  mucous  membrane  of 
the  upper  or  olfactory  region 
there  are  at  least  two  distinct 
types  of  cells,  neither  of  which 
have  cilia.  Some  are  cylindri- 
cal, with  branching  processes 
near  the  base.  These  cells, 
like  the  outer  cells  of  the  taste 
buds,  surround  and  support 
the  rod-shaped  olfactory  cells 
which  lie  between  them. 
The  latter  have  a  large  nucleus 
near  the  middle,  and  from  this 
region  of  the  cell  extend  two 
slender  processes;  one  runs  outward  between  the  cylindri- 
cal cells  and  projects  on  the  surface  of  the  mucous  membrane 
as  the  so-called  sensory  hairs,  the  other  seems  to  be  continu- 
ous with  branches  of  the  olfactory  nerve  (see  Fig.  134). 

Sensations  of  Smell.  —  During  ordinary  respiration  we  are 
not  often  conscious  of  sensations  of  smell.  When,  how- 
ever, we  perceive  an  odor,  we  can  increase  its  effect  by 
sniffing.  In  this  way  larger  quantities  of  air  are  drawn  up 
into  the  olfactory  regions  of  the  nose,  and  so  the  olfac- 
tory cells  are  stimulated  more  intensely.  The  olfactory 
sense  in  man  is  so  keen  that  three  one-hundred-millionths 
doooooooo)  °^  a  grain  of  musk  can  be  smelled. 


S/i.  PL 

FIG.  133.  —  Cross  Section  of  Nasal 
Chambers. 

An  =  cavities  in  upper  jaw  bone. 
Cr  =  perforations  in  ethmoid  bone 
through  which  pass  fibers  of 
olfactory  nerve. 
IT  =  lower  turbinate  bone. 
MT=  middle  turbinate  bone. 
ST=  upper  turbinate  bone. 
PI  =  hard  palate. 
Sp  =  partition      between      nasal 
chambers. 


298 


STUDIES  IN  PHYSIOLOGY 


o~ 


The  necessary  conditions  for  distinct  sensations  of  smell 
are  these :  (1)  The  odorous  materials  must  be  suspended  in 

the  air.  Even  when  the  nose 
cavities  are  filled  with  liquid 
cologne,  we  get  no  sensations 
of  smell.  (2)  The  mucous 
membrane  of  the  nose  must 
be  kept  moist.  In  cases  of 
catarrh,  when  the  amount  of 
mucus  is  lessened,  the  sense 
of  smell  is  either  lost  or  im- 
paired. (3)  The  olfactory 
cells  must  not  be  stimulated 
continuously.  After  one  has 
been  in  a  close  and  even  ill- 
smelling  room  for  a  time,  one 
ceases  to  detect  the  odor. 


FIG.  134.  —  Diagram  of  Lining  of 

Nose. 

A  =  cells  lying  close  together. 
B  =  two  cells  separated. 
c  =  cylindrical  (supporting)  cell. 
n  —  nucleus  or  nuclear  region  of 

cell. 

r  =  rod-shaped  (sensory)  cell. 
8  =  distal  region  of  cells. 


5.   THE  SENSE  OF  SIGHT 


Protection   for   the   Eye.  — 

The  delicate  organs  of  vision, 
the  eyes,  are  protected  in  a  wonderful  manner.  In  the  first 
place,  the  eyeballs  are  set  far  back  in  bony  sockets,  in  such 
a  way  that,  even  if  one  falls  forward  or  if  the  head  is  struck 
with  a  large  object,  there  is  little  danger  that  the  eyes 
themselves  will  be  hit.  Again,  each  eyeball  is  covered  by 
two  movable  lids  that  involuntarily  fly  together  when  any 
dangerous  object  approaches  the  head.  And,  finally,  the 
curving  eyelashes  on  the  edge  of  each  lid  protect  the  eye- 
ball to  a  considerable  extent  from  dust  and  dirt. 

The  Tear  Glands  and  Ducts.  —  The  exposed  surface  of  the 
eye  is  kept  moist  by  the  secretions  of  the  tear  glands.  The 
latter  lie  along  the  outer  side  of  each  eyeball,  and  are  about 
the  size  of  an  almond.  From  each  gland  the  salty  secretion 
oozes  out  on  the  under  surface  of  the  upper  eyelid,  and  as 


A  STUDY  OF  THE   SENSES  299 

the  eyelid  moves  automatically  at  frequent  intervals  over 
the  surface  of  the  eye,  the  exposed  portion  of  the  eyeball  is 
kept  from  drying. 

In  the  lower,  inner  corner  of  each  eye  one  can  detect  a 
small  elevation  or  papilla,  in  the  center  of  which  is  an  open- 
ing. This  is  the  beginning  of  a  tear 
duct  which  drains  off  into  the  nose 
cavity  the  excess  of  tears.  An  upper 
branch  of  this  duct  is  shown  in 
Fig.  135.  If  these  tubes  become 
stopped,  the  tears  drop  down  upon 
the  cheeks.  This  is  also  true  when 
an  increased  quantity  of  liquid  is  FlG.  135.  _ Front  View  of 
secreted  in  weeping.  Left  Eye,  with  Eyelid 

Sebaceous     Glands.  —  Along     the      partly  removed. 

edge  of  both  lids  are  numerous  oil          ^D  =  tear  duct. 

LG  =  tear  gland, 
glands.     Under  ordinary  conditions 

their  fatty  secretions  prevent  the  tears  from  flowing  out  of 
the  eyes.  At  times  these  sebaceous  glands  send  out  an 
abnormal  amount  of  secretion.  If  this  dries,  it  forms  a  yel- 
lowish rim  on  the  edge  of  each  lid,  which  may  temporarily 
glue  the  closed  eyelids  together. 

Movements  of  the  Eyes.  —  When  I  hold  my  head  still  and 
look  at  the  middle  region  of  the  opposite  wall  of  the  room,  I 
find  I  can,  by  moving  my  eyes,  look  at  the  ceiling,  at  the 
floor,  out  of  a  window  on  either  of  the  side  walls ;  I  can, 
also,  look  to  each  of  the  four  corners  of  the  walls  in  front  of 
me.  All  these  movements  of  the  eyeballs  are  accomplished 
by  the  separate  or  combined  action  of  the  six  muscles  which 
extend  from  each  eyeball  to  the  walls  of  the  eye  socket. 

Experience  tells  me  that  it  is  impossible  for  me  to  look 
in  one  direction  with  my  right  eye  and  in  the  opposite  direc- 
tion with  my  left.  The  two  eyes,  therefore,  work  together 
as  one,  and  all  the  motions  we  have  been  describing  are  con- 
trolled by  impulses  sent  out  from  the  brain  along  the  third, 
fourth,  and  sixth  pairs  of  nerves  (see  p.  279). 


300 


STUDIES  IN  PHYSIOLOGY 


General  Form  of  the  Eye.  —  If  the  six  muscles  be  severed 
near  their  attachment  to  the  eyeball,  the  eye  is  still  held  in 
place  by  the  large  optic  nerve,  which  enters  the  eyeball  from 
behind.  When  removed  from  its  socket,  each  eye  appears 
to  be  spherical  in  its  general  shape ;  but  a  closer  examina- 
tion shows  that  the  exposed  region  bulges  outward  some- 
what from  the  rest  of  the  eyeball. 


FIG.  136. 

A  =  muscles  of  right  eyeball  viewed  from  above. 

B  =  muscles  of  left  eyeball  viewed  from  outer  side. 
Ch  =  crossing  of  optic  nerves. 

11=  second  or  optic  nerves. 
///=  third  nerve  to  eye-muscles. 
ER,  Inf. Ob,  Inf.R,  S.Ob,  SR  =  muscles  that  move  the  eyeballs. 

Coats  of  the  Eye.  —  In  a  section  of  the  wall  of  the  eyeball 
one  can  make  out  three  coats.  The  outer  is  composed  of 
tough  connective  tissue.  The  portion  of  this  coat  which 
incloses  the  back  part  of  the  eyeball  is  called  the  sde-rot'ic 
(Greek  skleros  =  hard).  The  white  of  the  eye,  which  one 
can  see  beneath  the  eyelids,  is  the  front  region  of  this  scle- 
rotic coat.  The  bulging  part  of  the  eye,  to  which  we  have 
already  referred,  is  covered  by  a  portion  of  the  outer  coat, 
called  the  cor'ne-a  (Latin  corneus  =  horny).  Through  this 
hard  but  transparent  layer  one  can  see  the  colored  i'ris  and 
the  black  pu'pil. 


A   STUDY   OF   THE   SENSES 


301 


The  portion  of  the  second  coat,  which  lies  within  the 
sclerotic,  is  known  as  the  cho'roid.  It  is  richly  supplied 
with  blood  vessels,  which  run  through  meshes  of  connective 
tissue,  and  its  inner  layers  have  a  deep  black  color,  which  is 
due  to  dark  granules  of  pigment  much  like  those  described 
in  the  skin  (p.  235).  In  the  region  where  the  transparent 


Scl 


FIG.  137.  —  Diagram  of  the  Eye. 

c  =  cornea.  ON  =  optic  nerve. 

Ch  =  choroid  coat.  PE  =  pigment  beneath  retina. 
CP  —  ciliary  process.  R  =  retina. 

fc  =  yellow  spot.  Scl  =  sclerotic. 

I  =  iris.  spl  =  suspensory  ligament. 

L  =  lens.  VH  =  vitreous  humor. 

cornea  begins,  this  middle  layer  of  the  eye  separates  from 
the  outer  coat,  turns  inward,  and  forms  the  colored  portion 
of  the  eye  which  is  known  as  the  iris  (Greek  iris  =  rain- 
bow). In  the  center  of  the  iris  is  a  circular  perforation,  the 
pupil,  through  which  the  rays  of  light  pass  into  the  interior 
of  the  eyeball.  If  one  comes  suddenly  from  a  dark  into  a 
light  room,  one  sees  that  the  size  of  the  pupil  is  large,  but 


302  STUDIES   IN  PHYSIOLOGY 

that  soon  this  opening  decreases  in  size,  a  result  which 
is  brought  about  by  the  contraction  of  the  circular  in- 
voluntary muscles  found  in  the  iris. 

The  most  important  of  the  three  coats  of  the  eye  is  the 
inner,  which  is  known  as  the  ret'i-na;  for  it  is  this  layer 
which  is  acted  upon  by  the  rays  of  light  that  enter  the  eye. 
The  retina  is  only  about  one  eightieth  (-g^)  of  an  inch  in 
thickness,  and  yet  in  microscopical  sections  one  can  make 
out  ten  distinct  layers.  We  shall  not,  therefore,  attempt 
to  give  a  minute  description  of  this  complex  coat  of  the  eye. 
We  need  only  say  that  the  optic  nerve  passes  into  each  eye- 
ball through  the  sclerotic  and  choroid  coats  (Fig.  137),  that 
its  five  hundred  thousand  or  more  nerve  fibers  run  over  the 
inner  surface  of  the  retina,  and  that  each  nerve  fiber  finally 
comes  into  communication  with  certain  sensory  cells  lying 
just  inside  of  the  choroid  coat ;  the  cells  are  known  as  the 
rods  and  cones. 

The  Lens  of  the  Eye.  —  Behind  the  iris  is  the  crys'tal-Une 
lens,  a  beautiful  transparent  object,  both  surfaces  of  which 
are  convex.  It  is  highly  elastic,  and  is  attached  to  the 
cil'i-a-ry  muscles  of  the  choroid  coat  by  a  suspensory  liga- 
ment. In  a  later  section  we  shall  see  the  wonderful  ad- 
justments of  this  crystalline  lens  in  our  every  act  of  seeing. 

The  Humors  of  the  Eye.  —  Between  the  back  surface  of 
the  cornea  and  the  front  surface  of  the  iris  and  the  crystalline 
lens  is  a  small  cavity,  which  is  filled  with  a  watery  liquid, 
the  a'que-ous  hu'mor  (Latin  aquosus  =  watery  -f-  humor  = 
fluid).  Behind  the  crystalline  lens  is  another  cavity  of  con- 
siderable size.  This  is  distended  by  the  vit're-ous  hu'mor 
(Latin  vitreus  =  glassy),  which  is  perfectly  transparent  and 
resembles  jelly  in  its  consistency. 

The  Eye  as  a  Camera.  —  Any  one  who  is  at  all  familiar 
with  a  camera  knows  that  by  means  of  a  lens,  or  a  combi- 
nation of  lenses,  the  scene  to  be  photographed  is  made  to 
appear  upside  down  on  the  ground  glass  plate  at  the  back 
of  the  camera.  If  the  image  is  not  clear,  it  is  brought  into 


A  STUDY   OF  THE   SENSES 


303 


focus  by  moving  the  lens  nearer  to  or  farther  from  the 
plate. 

In  the  eye,  too,  we  have  an  arrangement  similar  to  that 
of  a  camera,  since  the  convex  surfaces  of  the  cornea  and 
crystalline  lens  bring  the  rays  of  light  to  a  focus  on  the 
sensitive  rods  and  cones  of  the  retina.  Since,  however,  it 
is  impossible  for  the  lenses  within  the  eye  to  be  moved 
backward  arid  forward,  focusing  or  ac-com-mo-da'tion  of  the 
eye  must  be  accomplished  in  a  different  way  j  namely,  by 
altering  the  shape  of  the  lens. 

A  B 


cm.  c.p 


FIG.  138.  —  Changes  in  Lens  in  Accommodation. 

A  =  adjustment  of  lens  for  distant  cm  =  ciliary  muscle. 

objects.  ch  =  choroid  coat. 

B  =  adjustment   of   lens  for  near  cp  =  ciliary  process. 

objects.  si  =  suspensory  ligament, 

c  =  cornea. 

Accommodation  of  the  Eye.  —  If  I  look  out  through  the  lace 
curtains  of  a  window  at  a  distant  object,  say  a  tree,  I  can 
see  the  latter  more  or  less  plainly,  but  the  meshes  of  the 
lace  appear  blurred.  When,  on  the  other  hand,  I  turn  my 
attention  to  the  individual  threads  of  the  curtain,  the  tree 
is  no  longer  distinctly  visible,  and  I  become  conscious,  too, 
of  a  feeling  of  muscular  effort.  What  takes  place  within 
the  eye  is  probably  this.  The  suspensory  ligament  is  con- 
stantly pressing  on  the  surface  of  the  crystalline  lens,  and 
so  tends  to  keep  its  outer  surface  more  or  less  flattened. 
This  condition  enables  the  lens  to  focus  clearly  on  the  rods 
and  cones  of  the  retina  images  of  distant  objects;  the 


304  STUDIES  IN  PHYSIOLOGY 

images  of  objects  near  at  hand,  however,  are  not  in  good 
focus,  and  so  they  appear  blurred.  Hence,  to  get  a  clear 
picture  of  something  close  in  front  of  me,  I  must  push  out- 
ward and  so  make  more  convex  the  outer  surface  of  my 
crystalline  lens ;  this  is  accomplished  by  the  contraction  of 
the  ciliary  muscles  of  the  choroid  coat,  to  which  we  have 
already  referred  (p.  302  and  Figs.  137  and  138). 

Sensations  of  Sight. — We  will  now  try  to  see  how  it  is 
that  the  eye  helps  us  to  get  sensations  of  sight.  If  an  ob- 
ject, say  an  arrow,  is  held  in  front  of  the  eye,  rays  of  light 
pass  in  a  great  many  directions  from  every  part  of  the 


FIG.  139.  —  The  Formation  of  an  Image  on  the  Retina. 

arrow  tip.  A  considerable  number  of  these  rays  strike  the 
convex  surface  of  the  cornea  and  the  crystalline  lens,  and 
are  thereby  focused,  or  made  to  converge  upon  a  point  on 
the  retina.  In  the  same  way  the  light  rays  from  every 
other  point  of  the  arrow  are  brought  to  focus  on  the  inner 
surface  of  the  retina.  By  this  means  a  smaller,  inverted 
image  of  the  arrow  is  projected  on  the  inner  lining  of  the 
eye.  The  influence  of  these  light  rays  then  passes  through 
the  transparent  layers  of  the  retina,  and  so  the  rods  and 
cones  become  stimulated. 

From  the  region  of  each  of  these  sensitive  cells  there  ex- 
tend back  into  the  brain  fibers  of  the  optic  nerve.  Most  of 
them  cross  on  the  ventral  surface  of  the  brain,  and  pass  to 
the  midbrain;  thence  fibers  run  backward  and  end  in  the 
cells  of  the  occipital  lobes  of  the  forebrain.  We  do  not  know 


A   STUDY   OF   THE   SENSES 


305 


what  kind  of  a   stimulus   this   is   that  affects  the    brain. 
While  we  may  say  that  an  inverted  image  of  the  objects 

x  • 

we  look  at  is  formed  011  the  retina,  we  cannot  liken  this 
to  an  impression  on  a  photographic  plate.  For  before  we 
get  any  sensations  of  sight,  the  impulse 
must  reach  the  cells  of  the  forebrain, 
and  we  are  sure  that  nothing  like  a 
photograph  is  taken  by  these  brain 
cells.  We  must  remember,  too,  that 
while  our  right  eye,  for  instance,  re- 
ceives an  inverted  image  and  sends 
impulses  to  the  left  half  of  the  brain, 
we  recognize  the  objects  which  we 
perceive  as  right  side  up  and  in  their 
proper  relations  in  space. 

The  Blind  Spot  and  the  Yellow  Spot.  — 
The  optic  nerve  does  not  enter  the 
eyeball  at  a  point  exactly  behind  the 
center  of  the  crystalline  lens  and 
cornea,  but  in  a  region  somewhat 
nearer  the  inidlme.  Since  the  optic 
fibers  pass  through  all  three  coats  and 
then  spread  over  the  inner  lining  of 
the  retina,  the  region  where  the  nerve 
enters  the  eye  is  without  any  rods  and 
cones.  The  following  simple  experi- 
ment proves  this  spot  to  be  blind.  If 
one  closes  the  left  eye,  holds  this  page  about  a  foot  away, 
and  looks  steadily  at  the  cross  near  the  top  of  the  page  with 
the  right  eye,  one  can  also  see  more  or  less  distinctly  the 
large  black  dot.  Let  the  book  be  slowly  brought  nearer, 
however,  and  the  cross  only  is  seen,  for  the  dot  has  disap- 
peared from  view.  If  the  page  is  brought  still  nearer  to  the 
eye,  both  cross  and  dot  are  seen  again. 


FIG.  140. 


306  STUDIES   IN  PHYSIOLOGY 

A  study  of  Fig.  140  will  make  clear  the  explanation  of 
these  facts  we  have  been  observing.  In  all  three  positions 
of  the  book  (A,  B,  C)  the  rays  of  light  pass  from  the  cross 
in  a  straight  line  through  the  cornea,  aqueous  humor,  lens, 
and  vitreous  humor,  and  reach  a  point  on  the  retina  directly 
behind.  This  is  the  region  of  keenest  vision,  for  here  the 
retina  is  thinnest  and  the  cones  are  most  numerous.  Since 
the  color  of  this  portion  of  the  retina  is  yellow,  this  is  called 
the  yellow  spot. 

In  position  A  the  rays  of  light  from  the  black  dot  enter 
the  eye  obliquely,  and  strike  the  retina  outside  the  yellow 
spot ;  hence  the  image  is  not  as  clear  as  is  that  of  the  cross. 
In  position  B  the  image  of  the  dot  falls  upon  the  interior 
end  of  the  optic  nerve ;  here  rods  and  cones  are  wanting, 
no  stimulus  is  sent  to  the  brain,  and  we  therefore  call  this 
the  blind  spot.  When  the  page  is  brought  to  position  (7,  the 
light  rays  from  the  dot  again  fall  upon  the  retina,  and  the 
dot  reappears  to  our  vision. 

Defective  Eyes.  —  A  normal,  healthy  eye  has  the  power  of 
adjusting  itself  so  that  objects  become  visible  which  are 

w  ithin  five  to  ten  inches,  or  those 
which  are  as  far  away  as  a  dis- 
tant horizon.  Many  people, 
however,  find  that  they  can  see 
objects  near  at  hand  much  more 
clearly  than  those  at  a  distance ; 
in  other  words,  they  are  near- 
sighted. Others,  on  the  other 
hand,  are  far-sighted.  These 
defects  in  vision  are  due  to  im- 
perfect formation  of  the  eyeball, 
•IG.  ltt._Tert^»  Astigma-  and  can  be  corrected  Qnly  by  the 

use   of   eyeglasses   or   spectacles, 

which  should  be  purchased  only  after  a  careful  examination 
of  the  eyes  has  been  made  by  a  specialist. 

Another  very  common  defect  of  the  eye  is  known  as  a-stig'« 


A   STUDY   OF  THE   SENSES  307 

ma-tism.  Many  people,  on  looking  with  each  eye  separately 
at  Fig.  141,  find  that  some  of  the  radiating  lines  stand  out 
sharply  defined,  while  others  are  indistinct  or  blurred.  In 
reality,  all  the  lines  are  equally  distant  from  each  other,  and 
the  indistinctness  referred  to  above  is  due  to  the  fact  that 
the  amount  of  curvature  is  not  the  same  in  all  regions  of  the 
cornea  and  crystalline  lens.  For  this  reason  some  of  the  rays 
of  light  are  not  brought  to  a  focus.  Astigmatism,  like  near 
and  far  sightedness,  should  be  corrected  by  the  use  of  proper 
glasses,  otherwise  the  constant  eye  strain  is  likely  to  cause 
chronic  headaches  and  other  disorders  of  the  body. 

Some  people,  too,  are  unable  to  distinguish  clearly  various 
colors ;  thus,  red  and  green  may  appear  the  same  to  them. 
In  other  words,  such  people  are  color  blind.  This  cannot  be 
corrected  by  glasses,  but  can  be  to  some  extent  by  training. 

Hygiene  of  the  Eyes.  —  The  eyes  have,  as  we  have  seen, 
wonderful  powers  of  adapting  themselves  to  varying  con- 
ditions. This  adaptability  often  leads  us  to  abuse  them. 
Thus,  we  frequently  read  when  the  light  is  insufficient,  we 
look  steadily  at  objects  until  we  suddenly  find  that  we  can- 
not see  clearly,  and  we  read  or  study  while  riding  in  swiftly 
moving  trains.  In  these  and  other  ways  we  compel  our  eyes 
to  make  adjustments  under  trying  conditions,  and  more  or 
less  eye  strain  is  sure  to  follow. 

When  we  read,  we  should  make  sure  that  the  light  is 
sufficient,  that  it  is  steady,  and  that  it  comes  over  the  left 
shoulder.  The  type  on  the  printed  page  should  be  little, 
if  any,  smaller  than  that  used  in  this  book  (ten-point  type), 
the  lines  should  not  be  close  together,  and  the  paper  should 
not  have  a  glossy  surface  to  reflect  the  light  into  the  eyes. 
One  should  remember,  too,  that  the  eyes,  like  other  organs 
of  the  body,  need  frequent  periods  of  rest.  Hence  study 
hours  should  be  followed  by  periods  in  which  the  eyes 
are  allowed  to  relax.  Pupils  who  have  defective  eyesight 
should  make  this  known  to  the  teacher,  and  should  be 
assigned  the  most  favorable  positions  in  the  schoolroom. 


308 


STUDIES  IN  PHYSIOLOGY 


6.   THE  SENSE  OF  HEARING 

The  External  Ear.  —  Attached  to  each  side  of  the  head  is 
an  oval,  more  or  less  flattened  expansion,  composed  largely 
of  cartilage  and  connective  tissue.  The  irregular  surface  of 
the  outer  portion  of  the  ear  doubtless  helps  somewhat,  like 
an  ear  trumpet,  to  converge  the  sound  waves  into  the  funnel  - 


FIG.  142.  — Parts  of  the  Eight  Ear. 

Note.  —  The  coils  of  the  cochlea  (S)  should  project  toward  the  observer. 
A  =  auditory  nerve  and  its  branches.    M  =  outer  portion  of  ear. 
B  =  semicircular  canal. 
G  =  tube  of  external  ear. 
I  =  utriculus. 
I'  =  sacculus. 


P  =  middle  ear  with  chain  of  bones. 

R  —  Eustachian  tube. 

S  =  cochlea. 

T  =  ear-drum  or  tympanum. 


like  canal.  This  is  about  an  inch  long,  and  leads  to  the  in- 
terior of  the  head.  In  the  lining  of  this  canal  are  certain 
wax  glands  ;  these  secrete  a  thin  fluid  which,  on  thicken- 
ing, hardens  into  a  yellow  paste,  the  earwax.  Across  the 
inner  end  of  this  tube  of  the  external  ear  is  stretched  a 
thin  membranous  partition,  known  as  the  eardrum,  or  tym'- 
pa-num  (Latin  tympanum  ==  drum). 


A  STUDY  OF  THE   SENSES 


309 


The  Middle  Ear.  —  Beyond  the  tympanum  is  a  small  cav- 
ity, known  as  the  middle  ear.  From  this  cavity  a  narrow 
tube  (the  Eustaehian  tube)  about  an  inch  and  a  half  long 
communicates  with  the  upper  part  of  the  throat  cavity.  If 
one  were  to  go  up  on  a  high  mountain,  one  would  find  that 
the  pressure  of  the  air  on  the  outside  of  the  body,  and  there- 
fore on  the  exterior  of  the  eardrum,  would  become  less,  and 
that  if  some  of  the  air  in  the  middle  ear  were  not  to  escape, 
the  eardrums  would  be  forced  outward,  and  hence  would  be 
ruptured.  If,  on  the  other  hand,  one  should  go  into  a  deep 
mine,  the  increased  pressure  on  the  outside  of  the  drums 
would  force  them  inward.  All  these  accidents  are  prevented 
by  the  presence  of  the  Eustaehian  tubes,  through  which  air 
can  pass  into  and  out  from  the  middle  ear,  and  so  the  pres- 
sure on  both  sides  of  the  tympanum  can  be  equalized.  In 
severe  head  colds,  as  we  have  already  seen  (p.  86),  the  open- 
ing from  the  throat  cavity  into  the  Eustaehian  tubes  becomes 
temporarily  closed.  We  then  are  conscious  of  a  ringing 
sensation  in  the  ears. 

The  Bones  of  the  Middle  Ear.  —  Within  the  cavity  of  the 
middle  ear  are  three  tiny  bones. 
The  first,  from  its  fancied  re- 
semblance to  a  hammer,  is 
called  the  mal'le-us  (Latin  mal- 
leus —  a  hammer) ;  the  second 
looks  somewhat  like  an  anvil, 
and  hence  is  known  as  the  in'cus 
(Latin  incus  =  an  anvil)  ;  the 
third  has  the  exact  form  of  a 
stirrup,  and  it  has,  therefore, 
received  the  name  sta'pes  (Latin  FIG.  143.  — Bones  of  Middle  Ear. 
stapes  =  a  stirrup).  These  three 
little  bones  are  arranged  in  a 
chain  across  the  cavity  of  the 
middle  ear,  for  the  handle  of  the  malleus  is  connected  with 
the  tympanic  membrane,  the  flat  part  of  the  stirrup  presses 


c  =  hammer  (malleus) . 
d  —  anvil  (incus). 
/=  stirrup  (stapes). 


310 


STUDIES  IN  PHYSIOLOGY 


•HS.C 


against  the  inner  ear,  and  the  incus  forms  the  connection 
between  these  two  bones  we  have  just  mentioned. 

General  Structure  of  the  Inner  Ear.  —  By  far  the  most 
complex  portion  of  our  auditory  apparatus  is  the  inner  ear. 
Indeed,  so  complicated  is  it  that  we  shall  not  attempt  to 
describe  minutely  its  various  parts.  In  general,  we  may 

say  that  the  in- 
ner ear  consists 
of  a  succession 
of  small  cavities 
hollowed  out  of 
the  interior  of 
the  hardest  part 
of  the  temporal 
bone;  that  with- 
in these  cavities 
lie,  more  or  less 
loosely,  a  series 
of  thin-walled 
tubes  and  small 
sacs  which  are 
distended  with 
a  watery  fluid 
known  as  en1- 
do-lymph  (Latin 
endo  =  within 
+  lymplia  =  wa- 
ter) ;  that  the  spaces  between  these  membranous  cavities  of 
the  ear  and  the  outer  bony  walls  are  filled  with  liquid  per'i- 
tymph  (Greek  peri  =  around  -f  Latin  lymplia  =  water)  ;  and 
that  finally,  and  most  important  of  all,  the  fibers  of  the 
eighth  or  auditory  nerve  run  to  certain  portions  of  the 
membranous  sacs  and  tubes  which  are  especially  sensitive 
to  sound  waves. 

The  Structure  and  Functions  of  the  Semicircular  Canals.  — The 
flattened  portion  of  the  stirrup  bone  is  fastened  to  a  thin- 


FIG.  144.  —  Distribution   of  Auditory  Nerve   (dia- 
grammatic) . 

A.N  =  auditory  nerve. 

ASC,  HSC,  PSC  =  a  swelling  on  each  of  the  semi- 
circular canals. 
av  =  canal  between  utriculus  and  sacculus. 

c  =  canal  between  sacculus  and  cochlea. 
Coch  =  cochlea. 
S  =  sacculus. 
U  =  utriculus. 


A  STUDY  OF  THE   SENSES  311 

walled  circular  membrane  which  helps  to  form  the  partition 
between  the  middle  ear  and  the  inner  ear.  Inside  of  this 
membrane  are  two  small  sacs,  the  u-tric'u-lus  (Latin  utric- 
ulus  =  a  little  skin  bottle),  and  a  still  smaller,  sac'cu-lus 
(Latin  sacculus  =  a  small  sac).  From  the  utriculus  run 
off  three  delicate  semicircular  canals.  When  we  are  stand- 
ing erect,  one  of  these  canals  in  each  ear  lies  in  a  hori- 
zontal position,  the  second  is  vertical  and  runs  anteriorly 
and  posteriorly,  while  the  third,  also  vertical,  extends  from 
side  to  side.  At  one  end  of  each  canal  is  a  little  swelling, 
to  which  runs  a  branch  of  the  auditory  nerve,  and  other 
branches  supply  portions  of  the  walls  of  utriculus  and 
sacculus.  The  cells  with  which  these  fibers  connect  are 
long  and  slender,  and  from  each  projects  into  the  endo- 
lymph  a  fine  hair.  Hence,  these  cells  resemble  some- 
what the  sensory  cells  which  lie  within  the  taste  buds  (see 
p.  295). 

If  I  were  sitting  on  the  deck  of  a  rolling  ship,  I  could 
tell,  even  with  my  eyes  closed,  in  what  direction  I  was 
being  rocked.  We  become  more  or  less  conscious,  too,  of 
the  ordinary  movements  of  the  head  without  the  use  of  the 
eyes,  and  the  impulses  that  give  us  these  sensations  prob- 
ably come  from  the  semicircular  canals  in  the  following 
way.  All  these  canals  and  their  enlargements,  together 
with  the  utriculus,  are  surrounded  by  perilymph,  and,  as 
we  have  said,  they  are  filled  with  endolymph.  When  the 
head  is  moved  in  any  direction,  for  instance,  in  walking, 
the  liquid  endolymph  flows  against  the  projecting  hairs  of 
the  sensory  cells,  and  an  impulse  is  thus  started  along  the 
auditory  nerve.  When  this  reaches  the  cells  of  the  fore- 
brain,  we  become  conscious  that  some  change  in  the  posi- 
tion of  the  body  is  taking  place.  After  we  have  learned  to 
walk,  however,  we  balance  our  body  without  any  conscious 
thought,  and  walking  becomes  automatic.  We  may  say, 
then,  that  the  part  of  the  ear  we  have  been  describing  gives 
us  a  knowledge  of  our  position  and  movements  in  space. 


312 


STUDIES  IN  PHYSIOLOGY 


The  Structure  and  Functions  of  the  Cochlea.  —  The  most 
complicated  portion  of  the  inner  ear  is  now  to  be  described. 


FIG.  145.  —  Diagram  of  a  Cross  Section  of  a  Coil  of  the  Cochlea. 

AN  =  auditory  nerve. 

CC=  central  compartment  of  cochlea  filled  with  endolymph. 

OC=  sensory  cells  with  long  projecting  hairs. 

Sc.T  and  Sc.V=  upper  and  lower  compartments  of  cochlea  filled  with 
perilymph. 

In  general  form  it  resembles  a  small  spirally  twisted  snail 
shell ;  hence  its  name  coch'le-a  (Greek  Jcochlias  =  a  snail)  (see 
Fig.  142).  Every  part  of  this  spiral  cavity  is  divided  by  two 


A  STUDY  OF  THE   SENSES  313 

thin  partitions  into  three  compartments ;  the  upper  and  lower 
are  filled  with  perilymph,  the  smaller  middle  one  contains 
endolymph.  The  latter  portion  of  the  cochlea  is  directly 
connected  with  the  cavity  of  the  sacculus,  and  hence  is  in 
communication  with  the  utriculus  and  semicircular  canals. 
Sensory  cells  with  long  projecting  hairs  are  found  on  the 
floor  of  the  central  cavity,  and  to  these  spirally  arranged 
cells  run  fibers  of  the -auditory  nerve. 

Sensations  of  Sound.  —  When  a  stone  is  dropped  into  a 
pond,  ripples  move  outward  in  circular  waves  over  the  sur- 
face, and  finally  disappear.  In  a  similar  manner  sound 
waves  are  transmitted  in  all  directions  from  a  given  body, 
say  a  bell  that  is  struck  and  caused  to  vibrate.  Some  of 
these  waves  of  air  enter  the  tube  of  the  external  ear,  cause 
the  tympanic  membrane  to  vibrate,  and  this  in  turn  sets  in 
motion  the  chain  of  small  bones  that  reach  across  the  cavity 
of  the  middle  ear.  The  movements  of  the  stirrup  bone  set 
in  vibration  the  thin  membrane  to  which  it  is  attached,  and 
so  the  perilymph  which  lies  in  the  inner  ear  becomes  dis- 
turbed. Since  the  perilymph  is  continuous  throughout  the 
cavities  of  the  inner  ear,  the  vibrations  which  have  been  set 
up  in  the  way  we  have  described  may  be  transmitted  in  all 
directions  throughout  the  bony  labyrinth. 

It  is  probable,  however,  that  these  waves  become  most 
effective  as  they  move  up  through  the  coils  of  the  cochlea, 
and  set  in  motion  the  thin  partitions  that  inclose  the  middle 
cavity.  When  the  endolymph  becomes  disturbed,  it  moves 
the  hairs  of  the  sensory  cells,  and  thus  an  impulse  is  finally 
started  along  the  fibers  of  the  auditory  nerve.  We  get  sen- 
sations of  sound  when  the  brain  cells  receive  and  interpret 
these  impulses. 

Loudness,  Pitch,  and  Quality.  —  The  various  sounds  of 
which  we  are  conscious  differ  in  loudness,  in  pitch)  and  in 
quality.  If  I  tap  a  bell  lightly,  I  cause  its  metal  to  vibrate 
only  a  little;  the  air  waves  that  influence  my  middle  and 
inner  ear  are  feeble,  and  I  can  scarcely  hear  the  sound. 


314  STUDIES  IN  PHYSIOLOGY 

A  hard  stroke,  on  the  other  hand,  results  in  a  loud  note. 
Hence,  loudness  depends  on  the  amplitude  of  the  vibrations. 
A  coarse  violin  string  that  vibrates  but  50  to  100  times  in 
a  second  produces  a  very  low  tone ;  when  the  number  is 
5000  to  10,000  per  second,  the  note  is  high.  The  pitch  of  a 
tone,  then,  depends  on  the  frequency  of  vibrations.  The 
power  of  different  individuals  to  distinguish  tones  varies 
greatly.  Some  can  hear  a  low  note  caused  by  as  few  as  30 
vibrations  per  second,  or  a  high  note  of  30,000  vibrations. 
The  movements  of  the  wings  of  some  insects  is  more  rapid 
even  than  this  high  rate ;  hence,  human  beings  cannot  hear 
the  sounds  they  produce. 

With  our  eyes  closed  and  at  some  distance  from  the  in- 
struments we  can  easily  tell  the  difference  between  the 
same  note  produced  by  a  violin  and  a  piano.  This  dif- 
ference is  not  one  of  loudness,  nor  of  pitch,  but  of  quality. 
When  a  violin  or  piano  string  gives  forth  a  sound,  the 
string  moves  as  a  whole,  and  so  produces  what  is  called  a 
fundamental  tone.  At  the  same  time  different  parts  of  the 
string  are  vibrating  more  or  less  independently,  and  partial 
or  over  tones  are  also  produced.  Hence,  the  air  waves  that 
are  set  in  motion  by  a  violin  string  are  a  result  of  a  funda- 
mental tone  combined  with  a  certain  number  of  overtones;  the 
piano  string,  on  the  other  hand,  while  it  can  give  out  the 
same  fundamental,  cannot  produce  the  same  combination  of 
overtones  as  does  the  violin. 


CHAPTER   XV 
A  STUDY  OF  THE  VOICE  AND  OF  SPEECH 

The  Vocal  Organs  of  Man.  —  Articulate  speech  is  one  of  the 
most  distinguishing  characteristics  of  mankind — indeed, 
we  may  say  that  man  is  the  only  animal  that  talks.  As  we 
might  expect,  a  rather  delicate  and  complicated  mechanism 
is  necessary  for  the  production  of  all  these  various  sounds. 
This  consists  of  three  parts :  namely,  the  lungs,  which  serve 
as  an  air  bellows ;  the  vibrating  membranes  known  as  the 
vo'cal  cords  (Latin  vox,  vocis  =  voice) ;  and  the  resonating 
chambers  of  the  throat,  nose,  and  mouth  chambers.  We 
have  already  discussed  (p.  213)  the  structure  and  action  of 
the  lungs.  We  shall  now  proceed  to  a  description  of  the 
voice  box  or  lar'ynx,  which  contains  and  regulates  the  vocal 
cords. 

The  Cartilages  of  the  Larynx.1  —  In  our  study  of  the  air 
passages  leading  to  the  lungs,  we  learned  that  the  windpipe 
is  kept  open  by  the  C-shaped  bands  of  cartilage,  which  we 
can  feel  on  the  ventral  surface  of  the  neck  region.  Crowning 
the  windpipe  and  opening  into  the  throat  cavity  is  the  larynx, 
the  walls  of  which  are  composed  of  movable  pieces  of  carti- 
lage. The  largest  of  these  is  the  thy'roid  (Greek  =  shield- 
shaped),  which  can  be  felt  on  the  ventral  surface  of  the  larynx 
or  "Adam's  apple."  The  two  halves  of  the  thyroid  are 
partly  united  on  the  ventral  surface,  curve  around  the  sides, 
but  leave  a  considerable  opening  dorsally.  Each  half  sends 

1  Most  of  the  structures  described  in  this  and  the  following  section 
can  be  demonstrated  to  the  class  by  using  the  windpipe  and  larynx  of 
a  sheep. 

315 


316 


STUDIES  IN  PHYSIOLOGY 


out  from  its  dorsal  border  an  anterior  projection  (which  be- 
comes connected  with  the  hy'oid  bone  at  the  base  of  the 
tongue)  and  a  posterior  process.  The  two  latter  processes 
fit  into  little  sockets  in  a  second  cartilage  of  the  larynx, 
known  as  the  cri'coid  (Greek  =  ring- 
shaped).  The  latter  surrounds  the 
posterior  portion  of  the  larynx  and 
has  the  form  of  a  signet  ring.  The 
flattened  part  of  this  band  of  carti- 
lage projects  anteriorly  between  the 
dorsal  edges  of  the  thyroid.  At- 
tached to  the  top,  outer  corners  of 
this  region  of  the  cricoid  are  two 
other  small  pieces  of  cartilage,  each 
known  as  a-ryt'e-noid  (Greek  =  ladle- 
shaped).  All  of  these  larynx  car- 
tilages are  movable  on  each  other, 
and  this,  as  we  shall  see,  is  a  device 
for  regulating  the  length  of  the 
vocal  cords  and  the  distance  between 
them. 

The  Vocal   Cords.  —  The    larynx, 
like  the  throat  cavity  and  the  wind- 

pipe. is  lined  with   mucous   mem- 
Fia.  146.  —The  Larynx  and    *  J 
Windpipe,  Ventral  View,     brane,  which  presents  an  even  sur- 

face except  in  the  region  near  the 
opening  into  the  throat.  Here  the 
lining  of  the  voice  box  is  pushed 
inward  to  form  two  rather  thick 
folds,  the  vocal  cords.  The  latter 


6,  6'  =  bronchi. 

c  =  cricoid  cartilage. 

e  =  epiglottis. 

h  =  hyoid  bone. 
t,  t'  =  thyroid  cartilage. 
tr  =  windpipe. 


are  not  like  strings,  as  their  name  implies;  rather,  they 
look  and  act  much  like  projecting  lips.  The  ventral  end 
of  each  fold  is  attached  to  the  inner  surface  of  the  thyroid 
cartilage,  and  behind  or  dorsally  each  is  fastened  to  one  of 
the  arytenoids  (Fig.  147). 

During  ordinary  breathing  the  two  arytenoids  are  pulled 


A  STUDY  OF  THE  VOICE  AND  OF  SPEECH       317 


apart  by  small  muscles,  and  a  V-shaped  opening  of  consider- 
able size  is  thus  left  between  the  vocal  cords.  Air  then 
passes  inward  or  outward  through  the  larynx  without  caus- 
ing any  sound.  When,  however,  we  wish  to  use  the  voice, 
in  singing  or  in  speaking,  the  two  arytenoids  are  pulled 
close  together  by  certain  muscles  of  the  larynx,  and  so  only 
a  narrow  space  is  left  between  the  cords.  Since  the  thyroid 
can  rock  backward  and  for- 
ward (by  means  of  its  lower 
pegs)  on  the  cricoid,  other  sets 
of  muscles  pull  the  arytenoids 
and,  the  thyroid  apart  from 
each  other,  and  by  this  means 
the  vocal  cords  are  tightened. 
We  then  force  air  outward 
from  our  lungs,  the  membra- 
nous cords  are  made  to  vibrate, 
and  a  sound  is  produced. 

Resonating  Cavities.  —  If  a 
violin  string  is  tightly 
stretched  across  the  corner  FIG.  147.— The 
of  a  room  and  is  then  set  in 
motion,  the  resulting  sound  can 
scarcely  be  heard.  But  when  a 
violin  is  played,  the  volume 
of  air  inclosed  by  its  thin 
wooden  walls  is  made  to  vi- 
brate as  well  as  the  string,  and 
the  loudiiess  of  the  sound  is 
thus  greatly  increased.  In  a  similar  manner  the  sound  of 
our  voice  depends  largely  on  the  vibrating  columns  of  air 
in  the  throat,  mouth,  and  nose.  Certain  bones  of  the  skull 
have  hollow  walls,  too,  which  increase  the  sound  produced 
by  our  vocal  organs. 

Speech.  —  The  words  of  which  spoken  languages  are  com- 
posed  consist   of   series   of  vowels  and  consonants.     The 


Glottis, 
from  above. 


viewed 


Ary  —  arytenoid  cartilages. 
Arp  =  muscles         between 

arytenoids. 

Cal,  Cap  =  muscles  from  ary- 
tenoids to  cricoid 
cartilages. 

Cr  =  cricoid  cartilages. 
Th  =  thyroid  cartilage. 
V=  vocal  cords. 


318  STUDIES  IN  PHYSIOLOGY 

vowels  are  a,  e,  i,  o,  and  u,  and  these  different  sounds  are 
produced  by  altering  the  shape  of  the  mouth  cavity  through 
movements  of  the  lips  and  cheeks.  In  none  of  these 
sounds  does  the  tip  of  the  tongue  touch  the  palate,  the 
teeth,  or  the  lips.  Many  of  the  consonants,  on  the  other 
hand,  are  pronounced  when  the  tongue  is  moved  against  cer- 
tain regions  of  the  walls  of  the  mouth.  Thus,  when  we 
utter  t,  d,  th,  or  n,  the  tongue  tip  presses  against  the  front 
teeth  and  hard  palate ;  these  consonants  are,  therefore, 
called  lin'gu-als  (Latin  lingua  =  tongue).  In  articulating  5, 
p,  and  ra  we  press  the  lips  together,  and  for  this  reason 
we  speak  of  these  consonants  as  la'bi-als  (Latin  labium  = 

HP). 

Loudness,  Pitch,  and  Quality. —  The  loudness  of  the  voice 
depends  upon  the  force  with  which  the  vocal  cords  and  the 
resonating  air  columns  are  made  to  vibrate.  In  whispering, 
faint  noises  are  produced  by  the  escaping  air  as  it  is  forced 
through  the  glottis  and  mouth  opening.  The  vocal  cords  do 
not  vibrate  when  we  whisper. 

When  a  high  note  or  tone  is  produced,  the  vocal  cords  are 
stretched  tightly  and  made  to  vibrate  rapidly.  Hence,  as  is 
the  case  in  other  instruments,  the  pitch  of  the  voice  corre- 
sponds to  the  rapidity  of  the  vibrations.  If  we  feel  of  the 
larynx  when  uttering  a  high  note,  we  become  conscious  that 
it  has  risen  a  little  toward  the  throat.  By  this  means  the 
resonating  chamber  becomes  shorter,  and  so  its  rate  of 
vibration  can  be  quickened  by  the  air  which  is  forced  from 
the  lungs.  In  early  life  the  resonating  chambers  and  the 
larynx  are  smaller,  and  the  vocal  cords  are  shorter  than  in 
later  years ;  for  these  reasons  the  pitch  of  a  child's  voice 
is  higher.  During  the  period  from  thirteen  to  sixteen  years, 
especially  in  boys,  the  rate  of  growth  in  this  region  of  the 
body  is  very  rapid,  and  so,  after  "the  voice  has  changed," 
its  tone  becomes  deeper. 

The  distinguishing  quality  of  an  individual  voice  depends 
on  the  combinations  of  fundamentals  and  overtones.  While 


A  STUDY  OF  THE  VOICE   AND  OF  SPEECH       319 

this  is  largely  a  result  of  the  size,  shape,  and  relative  posi- 
tions of  the  air  passages,  much  can  be  done  to  improve  the 
clearness  and  intensity  of  the  voice. 

The  Care  of  the  Voice.  —  "A  pleasing  speech  and  voice  are 
almost  equal  to  personal  appearance  in  importance  to  the 
individual  in  his  relations  to  others.  A  great  number  of 
complex  movements  are  needed  to  produce  proper  speech, 
and  these  are  acquired  slowly  and  with  difficulty.  .  .  . 
Speech  is  largely  the  result  of  imitation,  and  if  the  voices 
a  child  hears  are  harsh  or  coarse,  so  will  his  own  become. 
The  best  way,  therefore,  to  teach  a  child  distinct  and  re- 
fined speech  is  to  let  it  hear  such  only.  However,  this  is 
not  always  all  that  is  sufficient.  Enlarged  tonsils  and,  still 
more,  adenoid  vegetations  block  the  way  of  the  sound  waves 
to  the  nasal  cavities  after  they  leave  the  larynx.  This 
deprives  the  voice  of  both  intensity  and  resonance.  .  .  . 
The  number  of  people  that  are  allowed  to  grow  up  handi- 
capped by  hasty,  slurred,  harsh,  disagreeable  speech  and 
voice  is  great.  Parents  do  not  seem  to  appreciate  the 
advantage  to  their  children  in  after  life  that  a  refined, 
melodious  voice  will  be. 

"Proper  singing  is  one  of  the  best  modes  of  cultivating  a 
pleasant  speaking  voice,  even  if  the  singer  has  no  chance  of 
anything  more  than  a  place  in  a  chorus.  It  is  a  delight  to 
hear  a  good  singer  speak,  and  often  we  can  tell  that  a  per- 
son is  a  singer  simply  from  the  speech.  .  .  .  When  a 
child's  voice  is  changing,  singing  should  be  prohibited  until 
the  adult  type  of  voice  has  been  fully  developed.  This  is 
true  of  girls  as  well  as  boys.  Singing  is  an  excellent  form 
of  respiratory  gymnastics,  and  tends  to  develop  a  full,  well- 
formed  chest.  In  this  way  it  acts  as  a  preventive  of  lung 
diseases." — PYLE,  " Personal  Hygiene"  (W.  B.  Saunders 
&  Co.). 

Sounds  produced  by  Other  Animals.  —  The  song  of  some 
birds  is  most  remarkable  in  its  variety  and  richness.  We 
should,  therefore,  expect  a  highly  developed  larynx.  Such 


320  STUDIES   IN  PHYSIOLOGY 

is  not  the  case,  however,  for  the  music  of  birds  is  produced 
in  a  special  organ,  the  syr'inx  (Greek,  meaning  a  pipe), 
which  is  found  where  the  lower  end  of  the  windpipe  divides 
to  form  the  bronchi  (Fig.  146).  Here  the  air  tubes  enlarge, 
and  the  cartilage  rings  extend  little  more  than  half  around 
the  windpipe  and  the  bronchi.  Tense  membranes  complete 
the  wall  of  the  air  tubes,  on  their  inner  side,  and  act  as 
resonators.  Within  these  tubes  are  several  transverse  mem- 
branes which  are  vibrated  much  like  the  vocal  cords  of  man. 
The  trilling  note  of  certain  birds  is  probably  produced  by 
the  movements  of  a  semilunar  membrane  stretched  around 
the  sides  of  the  lower  part  of  the  windpipe. 

The  croaking  of  frogs  is  produced  by  vibration  of  vocal 
cords  at  the  sides  of  the  glottis  opening,  and  the  volume  of  the 
sound  is  largely  increased  by  the  resonating  cavities  formed 
by  the  lungs  and  the  croaking  sacs.  The  latter  open  near 
the  angle  of  the  jaws  on  either  side.  Most  reptiles  and 
fishes  produce  no  vocal  sounds  whatever. 

Among  the  group  of  insects  one  finds  many  different 
methods  of  producing  noises.  None  of  these,  however,  can 
be  called  vocal,  for  they  are  not  produced  by  organs  which 
resemble  at  all  a  larynx.  Flies,  mosquitoes,  and  many  other 
insects  produce  a  sound  by  the  rapid  movements  of  their 
wings ;  grasshoppers  scrape  the  rough  edges  of  their  wings 
together;  while  the  cicada  has  a  very  complex  organ  on  each 
side  of  its  body  by  which  it  produces  its  deafening  clatter. 


INDEX 


All  figures  refer  to  pages. 

A  *  before  a  figure  (for  example,  *310)  indicates  an  illustration  on  the  page  named. 

A  letter  n  after  a  figure  (for  example,  37  n)  refers  to  a  footnote  on  the  page  named. 


Abdominal  cavity,  92,  144. 
Abducted,  181. 
Abomasum,  *115,  116. 
Absorption,  101,  104. 

adaptations  for,  94,  95. 
Abstinence,  arguments  for,  70. 
Accidents  to  skeleton,  184. 
Accommodation  of  eye,  *303. 
Acids,  test  for,  14. 
Adam's  apple,  85,  210,  315. 
Adaptations, 

of  food  to  individual  needs,  107. 

shown  in  skull,  172. 

shown  in  spinal  column,  166. 
Adducted,  181. 

Afferent  nerves,  *258,  264,  *266. 
Air,  amount  of,  6. 

changes  due  to  respiration,  222. 

composition,  10,  14,  *15. 

how  lungs  are  filled  with,  218. 

passages,  85,  *211. 

pressure,  11,  12. 

sacs  in  lungs,  211,  *215 

study  of,  11-15. 
Albumin,  see  Proteids. 
Albuminous    substances,    see    Pro- 
teids. 
Alcohol,  as  a  stimulant,  etc.,  66-74. 

composition,  66  n. 

danger  in  use  of,  69,  109. 

effect  on  circulation,  154. 

effect  on  dogs,  71-74. 

effect  on  digestion,  109. 

effect  on  nervous  system,  285. 

effect  on  temperature,  243. 

in  patent  medicines,  39. 

life  insurance  and,  70-71. 

preparation  of,  36. 


Alimentary  canal, 

absorption  from,  101—104. 

of  bird,  *114. 

of  earthworm,  *112. 

of  frog,  *113. 

of  sheep,  *115. 

parts  of,  75,  *76. 
Ammonia,  44. 
Amoeba,  23,  *24. 

cell  division,  30,  *31. 

locomotion,  205. 

nervous  functions,  287. 

nutrition  in,  *117. 

respiration  of,  229. 
Amphibia,  see  Frog. 

corpuscles  of,  *126. 

skin  of,  244. 
Anaemia,  124. 
Anatomy,  2. 

also    see   Alimentary    canal    of 
bird,  earthworm,  reptile,  etc. 
Ankle  joint,  181. 
Anterior,  20. 
Antitoxin,  224. 
Antlers,  247. 
Anvil  (incus)  bone,  *309. 
Aorta,  134,  *143,  *145. 
Aortic  arches,  *112,  154. 
Apex  of  heart,  130. 
Appendages,  20,  21. 
Appendicitis,  96. 
Appendix,  vermiform,  *76,  96. 
Aqueous  humor,  302. 
Arachnoid,  257,  273. 
Arm,  skeleton  of,  160,  *163. 

control  of  movements,  280. 

of  child,  173. 
Arterial  blood,  147. 


321 


322 


INDEX 


Arteries,   see  Aorta,   Carotid,    etc. 
Artery,  129,  137. 

effect  of  heat  and  cold  on,  151. 

structure  of,  *137. 
Articular  processes,  *165. 
Artificial  respiration,  225. 
Arytenoids,  cartilages,  316,  *317. 
Ascending  colon,  *76,  96. 
Assimilation,  29. 
Astigmatism,  306. 

test  for,  *306. 
Atlas  vertebra,  *166. 
Atmosphere,  pressure  of,  6. 
Atwater,  Prof.  W.  O.,  42  n,  66. 
Auditory  nerves,  of  frog,  269. 

of  man,  279,  *307,  310. 
Auricle,  *130,  131,  *132. 
Axis  vertebra,  *166. 

cylinders,  285,  258. 

Bacillus  tuberculosis,  224. 
Backbone,  see  Spinal  column. 
Bacteria,  *32-33. 

changes  caused  by,  32. 

conditions  for  growth,  34. 

reproduction  of,  34. 

study  of,  32-35. 
Ball-and-socket  joints,  180. 
Bathing,  240. 
Baths,  240-241. 
Bats,  locomotion  of,  207. 
Beat  of  heart,  134. 
Beef  blood,  118-121. 
Belly  of  muscle,  195. 
Biceps  muscle,  *194. 
Bicuspid  (premolar)  teeth,  78. 
Bile,  99. 

duct,  *76,  99. 
Biology,  3. 
Birds,  alimentary  canal,  *114. 

brain  of,  *289. 

circulation  of,  157. 

feathers  of,  *245. 

locomotion  of,  207. 

respiration  of,  230. 

skeleton  of,  189. 

skin  of,  245. 

song  of,  319. 

syrinx  of,  320. 
Bladder,  urinary,  240. 
Blood,  corpuscles  of,  23,  *25,  26. 

manufacture,  75-116. 


Blood,  corpuscles  of — Continued. 

plasma,  26. 

regulation  of  supply,  148. 

serum,  127. 

study  of,  117-128. 

vessels,  129,  137-142. 
Blood  supply,  to  bones,  176. 

dermis,  *234,  235. 

epidermis,  233. 

hair,  237. 

heart,  136. 

kidneys,  *250. 

lungs,  *215. 

mucous  membrane,  77. 

muscles,  *198. 
Blushing,  280. 
Body,  as  a  machine,  2. 

chemical  composition,  16. 

of  vertebra,  165. 

regions  of,  20. 
Boiling  meats,  53. 

vegetables,  55. 
Bones,  23,  *27. 

structure  of,  174-176. 

study  of,  159-192. 
Bony  framework,  uses  of,  159. 
Botany,  4. 
Brain,  21,  *254. 

of  frog,  268-273. 

of  man,  273-283. 
Bread,  composition  of,  41. 

making  of,  56. 
Breastbone  (sternum),  168,  *173. 

of  child,  173. 
Broiling  meats,  54. 
Bronchial  tubes,  211. 

arteries,  215. 
Bronchitis,  223. 
Bronchus,  *211. 
Bruises,  treatment  of,  153. 
Budding  of  yeast,  *27.. 
Burning,  see  Oxidation. 
Burns,  treatment  of,  242. 

Cfficum,  *22,  *76,  96. 
Calomel,  100. 
Calorie,  51. 
Calorimeter,  51. 
Camera,  eye  as,  303. 
Canine  teeth,  78. 
Capillaries,  129,  138-*141. 
of  frog's  foot,  141. 


INDEX 


323 


Carbohydrates,  17. 

amount  needed  per  day,  56. 

presence  in  vegetable  food,  47. 

used  in  proteid  manufacture,  50. 

uses  of,  51. 
Carbon,  in  carbohydrates,    17. 

in  fats,  17. 

in  proteids,  18,  50. 

in  starch  manufacture,  47. 

properties  of,  7. 
Carbon  dioxid,  composition,  9. 

given  off  by  lungs,  210. 

in  starch  manufacture,  48. 

preparation  of,  7. 

produced  in  body,  16,  17,  18. 

produced  by  yeast,  36. 

properties,  8. 

removal  from  body,  19,  210. 

symbol,  9. 

test  for,  8,  16. 
Cardiac  orifice,  88. 
Care  of  voice,  319. 
Carotid  artery,  143. 
Carpal  bones,  160. 
Carron  oil,  242. 
Cartilage,  *27. 

of  larynx,  *315. 

of  windpipe,  *214. 
Cells,  23,  25,  26,  *28,  39. 

as    units   of    living    substance, 
23-32. 

division  of,  30. 

of  bacteria,  *32. 

of  leaf,  48. 

of  spinal  cord,  *258. 

of  yeast,  *37. 
Cellulose,  25. 

in  bacteria,  33. 
Cement  substance,  80. 
Centrum  of  vertebra,  165. 
Cerebellum,  comparison  of,  *290. 

of  frog,  269. 

of  man,  275. 

Cerebral   hemispheres,    comparison 
of,  289. 

of  frog,  268,  272. 

of  man,  274. 
Cerebro-spinal  fluid,  257. 

nerve  center,  254. 
Cervical  enlargement,  256. 

nerves,  261. 
vertebra,  162. 


Changes  due  to  respiration,  231. 

in  blood,  147. 
Cheek  bones,  171. 
Chemical  composition,  of  air,  *15. 

alcohol,  66  n. 

blood,  127. 

body,  16-19. 

bones,  177-178. 

glycogen,  17  n. 

grape  sugar,  17  n. 

hemoglobin,  18  n. 

inspired  and  expired  air,  221- 
223. 

protoplasm,  28. 
Chemistry,  4,  16. 
Chest  cavity,  216-220. 
Child  skeleton,  172-174. 

nervous  system,  283. 
Chlorate  of  potassium,  11,, 
Chlorophyll  bodies,  48. 
Choking,  225. 
Chordae  tendinese,  132. 
Choroid  coat,  300. 
Cicada,  noise  of,  320. 
Cilia,  33,  206. 

in  windpipe,  213,  *214. 
Ciliary  muscle,  302. 
Circulation  of  the  blood,  129-158. 
Circumducted,  181. 
Circumvallate  papillae,  295. 
Classification,  of  bones,  176. 

joints,  180. 
Clavicle,  169. 
Claws,  247. 
Clot  of  blood,  118. 
Clothing,  kinds  of,  242-243. 

and  respiration,  223. 
Coagulation  of  blood,  119,  121. 
Coats  of  the  eye,  300-302. 
Coccygeal  nerves,  261. 
Coccyx,  165. 
Cochlea,  312-313. 
Coffee,  64. 
Colds,  152,  223. 
Collar  bones,  169. 
Colloids,  103. 
Colon,  *76,  96. 
Colony,  of  bacteria,  33. 

of  yeast,  38. 
Color  blindness,  307. 

of  blood,  125. 
Commissure  of  cord,  258. 


324 


INDEX 


Comparative  study,  of  blood,  125- 
127. 

circulation,  154-158. 

digestion,  109-116. 

excretory  organs,  251—252. 

locomotion,  205-208. 

nervous  system,  287-290. 

respiration,  229-231. 

skeleton,  186-192. 

skin,  244-247. 
Compounds,  9. 
Connective  tissues,  23,  *180. 
Conscious  activities,  280. 
Constipation,  prevention  of,   108. 
Consumption,  224. 
Convolutions,  275,  290,  *274. 
Cooking  of  food,  52-56. 
Cooperation  of  organs,  253. 
Coral,  *186. 
Coronary  arteries,  137. 
Corpuscles  of  blood,  *25. 

red   corpuscles,    *25,   26,    *122, 
*126. 

white  corpuscles,  26,  122,   126. 

tactile,  235,  *291. 
Cortex,  of  brain,  276. 

of  kidney,  249. 
Coughing,  225,  280. 
Cranial  nerves,  of  frog,  269. 

of  man,  278-279. 
Cranium,  170. 
Crayfish,  *188. 

green  glands  of,  252. 
Cribiform  plate,  296. 
Cricoid  cartilage,  316. 
Croaking  sacs  of  frog,  320. 
Crop,  of  bird,  115. 

of  earthworm,  113. 
Croup,  223. 
Crown  of  tooth,  79. 
Crystalline  lens,  302. 
Crystalloids,  103. 
Cuts,  treatment  of,  153. 

Dandruff,  241. 

Danger  in  use  of  alcohol,  69. 

Daughter  cells,  of  amoeba,  31. 

of  yeast,  38. 
Defibrinated  blood,  120. 
Dental  formula,  79. 

of  dog,  111. 

of  horse,  111. 


Dental  formula  —  Continued. 

of  milk  set,  79. 

of  permanent  set,  79. 

of  rabbit,  110. 
Dentine,  80. 

Deoxygenated  blood,  148. 
Dermis,  235-236. 
Descending  colon,  *76,  96. 
Diaphragm,  21,  *211. 

movements  of,  216. 

of  rabbit,  *22. 
Diet,  56-57. 
Digestion,  75. 

hygiene  of,  106-109. 

in  intestines,  93. 

of  fats,  97-98. 

of  insoluble  salts,  91. 

of  proteids,  91,  97. 

of  soluble  salts,  84. 

of  starch,  84,  97. 

of  sugar,  84. 

synopsis  of,  105. 
Digestive  glands,  75. 
Diphtheria,  223. 
Disease  germs,  35. 
Dislocations,  185. 
Distillation,  36. 
Distilled  liquors,  39. 
Division  of  cell,  30. 
Dog,  brain  of,  289. 

dental  formula,  111. 
Dorsal,  21. 

horns  of  gray  matter,  *258. 

nerves,  261. 

roots  of  nerves,  261,  264. 

vertebrae,  162. 
Ducts  of  plants,  47. 
Dura  mater,  257,  273. 
Dusting,  228. 

Ear,  308-314. 

drum,  308. 

wax,  308. 
Earthworm,  *112. 

alimentary  canal,  112. 

circulation,  154. 

excretion,  252. 

locomotion,  206. 

nervous  system,  287. 

respiration,  229,  230. 
Eating,  hygienic  habits  of,  106. 
Economy  of  foods,  57-60. 


INDEX 


325 


Efferent  nerves,  *258,  264,  *266. 
Elements,  8,  9. 
Emulsion,  97. 
Enamel  of  tooth,  79. 
Endolymph,  310,  311. 
Energy,  production  of,  29. 
Engine,  compared  to  body,  1,  29. 

oxidation  in,  17. 
Epidermis,  233-235. 
Epiglottis,  85. 
Esophagus,  *85,  87. 
Ethmoid  bone,  170,  296. 
Eustachian  tubes,  86,  309. 
Excretion,  251. 
Exercise,  effect  on  blood,  123. 

circulation,  152. 

muscles,  203. 

respiration,  222. 
Expiration,  209,  219. 
Extend  (joint),  181. 
Extensor  muscle,  195. 
External  ear,  308. 
Eye,  298-307. 

lids,  299. 

Face,  bones  of,  171. 
Fang  of  tooth,  79. 
Far-sighted  eyes,  306. 
Fats,  absorption  of,  95,  100. 

amount  in  body,  17. 

amount  needed  each  day,  56. 

digestion  of,  97-98. 

effect  of  heat  on,  17. 

in  protoplasm,  28. 

test  for,  44. 

uses  of,  17,  51. 
Fehling's  solution,  45  n. 
Femur,  162. 
Fermentation,  37. 
Fibers,  of  muscle,  198. 

of  nerves,  *259. 
Fibrin,  119. 
Fibrinogen,  120. 
Fibula,  162. 
Filiform  papillae,  294. 
Fish,  brain  of,  289. 

circulation,  *155. 

locomotion,  207. 

respiration,  229, 

skeleton,  188. 

skin  of,  244. 
Fissures,  256. 


Fissures  —  Continued. 

of  Rolando,  275. 

of  Sylvius,  275. 
Flat  bones,  177. 
Flex  (joint),  181. 
Flexor  muscle,  195. 
Flies,  noise  of,  320. 
Focus  on  retina,  304. 
Fontanelle,  172. 
Foods,  41. 

adaptation  to  individual  needs, 
107. 

alcohol  as  a,  66-68. 

and  muscles,  202. 

and  nervous  system,  284. 

and  skeleton,  182. 

composition  of,  41—44,  *43. 

cooking  of,  52—56. 

economy  of,  57—60. 

nutrients  in,  41,  *43. 

refuse  in,  42. 

uses  of,  in  body,  30,  41. 
Foramen  magnum,  170. 
Forebrain,  of  frog,  268. 

of  man,  275. 
Fractures,  184. 
Frog,  alimentary  canal,  *113. 

brain  of,  *269. 

circulation  of,  *156. 

corpuscles  of,  *125. 

croaking  of,  320. 

flow  of  blood  in  foot,  *141. 

locomotion  of,  207. 

nervous  system,  268-273,  289. 

respiration,  229. 

skeleton  of,  *189. 

skin  of,  244. 
Frontal  bone,  170. 

lobes  of  brain,  275. 
Fuel  value  of  nutrients,  51. 
Function,  21. 

of  all  protoplasm,  40. 
Fungiform  papillae,  294. 

Gall  bladder,  *76,  *99. 
Ganglion,  262. 

of  brain,  276. 

of    sympathetic    nervous    sys- 
tem, 266. 
Gastric  artery,  144. 

glands,  *88. 

juice,  88. 


326 


INDEX 


Gelatin,  53. 
General  senses,  293. 
Girdles  of  skeleton,  168-170. 
Gizzard,  of  bird,  115. 

of  earthworm,  113. 
Glands,  digestive,  75. 

gastric,  *88. 

of  the  skin,  238. 

salivary,  82. 
Gliding  joints,  182. 
Glosso-pharyngeal  nerves  of  frog, 
269. 

of  man,  279. 
Glottis,  210. 
Glycerin,  97. 
Glycogen,  17,  100. 

composition  and  symbol,  17  n. 
Gray  matter,  258. 
Grape  sugar,  17. 

composition  and  symbol,  17  n. 

test  for,  45. 

Grasshopper,  noise  of,  320. 
Gristle,  see  Cartilage. 
Growth,  29. 
Gullet,  see  Esophagus. 
Gums,  77. 

Habits,  282. 

of  breathing,  222. 

of  eating,  106. 
Habitual  activities,  281. 
Hair,  232,  236-238,  *237. 

care  of,  241. 

of  mammals,  247. 
Hammer  (malleus)  bone,  *309. 
Hangnails,  241. 
Hard  bone,  175. 

palate,  77. 
Haslet,  213. 
Head,  skeleton  of,  170. 

of  bones,  175. 

Hearing,  sense  of,  308-314,  380. 
Heart,  21,  129-137.    . 

and  lungs,  *130. 

muscle,  *202. 

of  rabbit,  *22. 
Heat  regulation,  239. 
Hemoglobin,  composition  of,  18  n. 

use  of,  122. 

Hepatic  artery  and  vein,  146. 
Hilum  of  kidney,  248,  *249. 
Hindbrain,  268. 


Hindbrain  —  Continued. 

of  frog,  269,  271. 

of  man,  275. 
Hollow  bones,  advantage  of,   176. 
Hoofs,  247. 
Horns,  247. 

of  gray  matter,  258. 
Horse,  skeleton  of,  *190. 

foot  of,  *191. 

locomotion  of,  208. 
Humerus,  160. 
Humors  of  the  eye,  302. 
Hunger,  sensations  of,  294, 
Hydrochloric  acid,  89. 

action  on  bone,  178. 
Hydrogen,  in  carbohydrates,  17. 

in  proteids,  18. 

oxidation  of,  10. 
Hygiene,  of  blood,  123-124. 

of  circulatory  system,  151—154. 

of  digestion,  106-109. 

of  the  eyes,  307. 

of  muscles,  202-205. 

of  nervous  system,  283-286. 

of  respiratory  organs,  222—228. 

of  skeleton,  182-184. 

of  skin,  240-243. 

of  voice,  319. 
Hyoid  bone,  316. 

Ilio-co3cal  orifice  and  valve,  96. 

Impulses  (nervous),  264. 

Incisor  teeth,  78,  80. 

Incus  bone,  309. 

Inferior  vena  cava,  133,  144,  *145. 

Inner  ear,  310. 

Insects,  noises  of,  320. 

Insertion  of  muscle,  195. 

Inspiration,  209,  219. 

Intemperance,  cost  of,  71. 

Intercellular  substance,  27. 

Inter  vertebral  foramina,   168,  260. 

Intestines,  21,  *76,  92-96. 

absorption  in,  104. 

of  mouse,  *94. 

of  rabbit,  *22. 
Invertebrates,  20. 

classes  of,  20. 

kidneys  of,  252. 

nervous  system  of,  288. 

skeleton  of,  187. 

skin  of,  244. 


INDEX 


327 


Involuntary  muscle,  90,   194,  201, 

*202. 
Iodine,  solution,  45  n. 

symbol,  9. 
Iris  of  the  eye,  301. 
Iron  in  hemoglobin,  18  n. 

symbol,  18  n. 
Irregular  bones,  177. 

Jaundice,  99. 
Jawbones,  171. 
Joints,  179-182. 
Jugular  veins,  144. 

Kidneys,  21,  248-252. 

excretion  of  urine,  18. 
Kinds  of  muscle,  193. 
Kneecap,  162. 

Labial  consonants,  318. 
Lac  teals,  *95,  151. 
Large  intestines,  *76,  96. 
Larynx,  210,  212,  314. 

of  birds,  319. 

Lateral  processes  of  vertebra,  165. 
Laws,  pure  food,  46. 
Leg,  bones  of,  162. 

movements  of,  281. 

of  child,  174. 

Lens  of  the  eye,  302,  *303. 
Life  insurance,  70-71. 
Ligaments,  179. 

Lime  water,  as  test  for  carbon  di- 
oxid,  8,  210. 

preparation  of,  8  n. 
Lingual  consonants,  318. 
Liquors,  distilled,  39. 

malt,  38. 

Litmus  paper,  14. 
Liver,  21,  98,  *99. 

as  an  excretory  organ,  252. 

glycogen  in,  17. 

of  rabbit,  *22. 

Living  substance,  see  Protoplasm. 
Localization  of  functions  in  brain, 

280-281. 
Locomotion,     comparative    study, 

205-208. 

Locomotive,  see  Engine 
Long  bones,  176. 
Loudness  of  sound,  313,  318. 


Lumbar  enlargement  of  cord,  256. 

nerves,  261. 

vertebra?,  162. 
Lungs,  21,  213-216. 

as  excretory  organs,  251. 

of  rabbit,  *22. 
Lunula,  236. 
Lymph,  148-149. 
Lymphatic  nodes,  *151. 

system,  148-151. 
Lymphatics,  *149. 

Malar  bones,  171. 
Malleus  bone,  309. 
Malt  liquors,  38. 
Mammals,  247. 

anterior  appendages  of,  190^ 
Mandible,  171. 
Marrow,  175. 
Match,  study  of,  5-10. 
Meats,  composition  of,  42. 

cooking  of,  52—54. 
Medicines,  patent,  39. 
Medulla  oblongata,  comparison  of, 
290. 

of  frog,  269. 
Medullary  region  of  kidney,  248. 

sheath,  259,  283. 
Memory,  280. 
Mesenteric  arteries,  144. 
Mesentery,  *93. 
Metabolism,  30. 
Metacarpal  bones,  160. 
Metatarsal  bones,  162. 
Miclbrain,  of  frog,  268,  271. 

of  man,  275. 
Middle  ear,  309. 

Mineral     substances,     amount     in 
body,  16. 

digestion  of,  84,  91. 

test  for,  8,  46. 

uses  of,  52. 
Mitral  valve,  132. 
Molar  teeth,  78. 
Mosquito,  noise  of,  320. 
Motor  cells  and  fibers,  278. 
Mouth  cavity,  77,  *81. 

absorption  in,  103. 
Mucous  membrane,  77. 
Mucus,  77. 
Muscles,  23. 

of  esophagus,  87. 


328 


INDEX 


Muscles  —  Continued. 
of  eyes,  299. 
of  intestine,  93. 
of  stomach,  90. 
of  tongue,  82. 
study  of,  193-208. 

Nails,  232,  *236. 

care  of,  241. 
Narcotics,  63. 
Nasal  bones,  171. 

"  cavities,  296. 
Near-sighted  eyes,  306. 
Neck  of  tooth,  80. 
Nerve  centers,  254,  262. 

cells,  *259,  263,  277,  (of  child), 
283,  number  of,  284. 

fibers,  *259,  263-264. 

impulses,  264,  277. 

trunks,  254. 
Nerves,  23,  256. 

of  frog,  269-270. 

of  hair,  237. 

of  muscles,  199. 

of  skin,  235. 

of  stomach,  heart,  etc.,  267. 

spinal,  260-266. 
Nervous  system,  253,  290. 
Neural  arch,  165. 

ring,  *165. 
Nitric  acid,  44. 
Nitrogen,  amount  in  air,  24. 

in  nitrogenous  substances,  18. 

preparation,  *13. 

properties,  15. 

use  in  air,  15. 
Nitrogenous   substances,    see   Pro- 

teids. 

Noises  of  insects,  320. 
Nosebleed,  153. 

cavity,  211,  297. 
Nucleus,  25. 
Nutrients,  41. 

fuel  value,  of,  51-52. 

in  various  foods,  *43. 

tests  for,  44. 

uses  of,  50-52. 
Nutrition,  in  amoeba,  117. 

in  man,  117. 

Occipital  bones,  170. 
convolutions,  280. 


Oil  glands,  238. 

Olfactory  lobes  and  nerves,  of  frog, 
268. 

of  man,  275,  289. 

comparison  of,  290. 

region  of  nose,  297. 
Optic  lobes  and  nerves,  of  frog,  268. 

of  man,  275,  279,  300. 

comparison  of,  290. 
Organism,  39. 
Organs,  21,  39. 

of  plants,  47. 
Origin  of  muscle,  195. 
Osmic  acid,  44  n. 
Osmosis,  101-103. 
Oxid,  of  carbon,  7. 

of  hydrogen,  7. 

of  manganese,  11. 

of  phosphorus,  5,  13,  14. 

of  sulphur,  7. 
Oxidation,  10. 

in  body,  16,  17,  19,  29,  50,  51 

of  alcohol,  66-68. 

of  carbon,  7,  8. 

of  fats  in  the  body,  17. 

of  phosphorus,  6. 

of  sulphur,  7. 
Oxygen,  amount  in  air,  14. 

effect  on  blood,  121. 

in  carbohydrates,  17. 

in  proteids,  17. 

in  starch   manufacture,   48-49. 

preparation,  *11. 

properties,  12. 

use  in  air,  13. 

use  in  body,  16,  17. 
Oxygenated  blood,  147. 


Pain,  sensations  of,  293. 
Palate  bones,  171. 

hard,  77. 

soft,  77. 

Pancreas,  21,  97-98. 
Pancreatic  juice,  97. 
Papillae,  of  dermis,  235. 

of  tongue,  82,  294. 
Papillary  muscles,  133. 
Paramecium,  205. 
Parietal  bones,  170. 
Parotid  glands,  82. 
Patella,  162. 


INDEX 


329 


Patent  medicines,  composition  of, 
39. 

use  of,  108. 
Pectoral  girdle,  169. 
Peculiarities    of    human    skeleton, 

192. 
Pelvic  girdle,  170. 

bones,  170. 
Pelvis  of  kidney,  248. 
Pepsin,  89. 
Peptone,  91. 
Pericardium,  130. 
Perilymph,  310. 
Perimysium,  197. 
Perineurium,  262. 
Periosteum,  174. 
Peritoneum,  92. 
Peritonitis,  92. 
Perspiration,  239. 
Perspiratory  glands,  238. 
Phalanges,  160,  162. 
Phosphorus,  5,  13. 
Physical  properties,  12. 
Physics,  4. 
Physiology,  3. 
Pia  mater,  257,  273. 
Pigment  spots,  235. 

of  eye,  301. 

Pitch  of  sound,  314,  318. 
Pivot  joints,  182. 
Plants,  cells  of,  25  n. 

manufacture  of  food  by,  47. 

organs  of,  47. 
Plasma  of  blood,  26,  120. 
Pleura,  216. 
Pleurisy,  225. 
Pneumonia,  223. 
Poison,  62. 

alcohol  as  a,  69. 
Pons  Varolii,  275. 
Pores  of  sweat  glands,  223. 
Portal  system,  145. 
Posterior,  21. 
Premolar  teeth,  78. 
Pressure,  on  bones,  183. 

of  the  atmosphere,  12. 
Primitive  sheath,  259. 
Processes  of  vertebrae,  165. 
Proteids,  18. 

amount  needed  each  day,  56. 

digestion  of,  91,  97. 

in  protoplasm,  28.. 


Proteids  —  Continued. 

manufacture  of,  by  plants,  50. 

tests  for,  44. 

uses  of,  50. 
Protein,  42  n. 
Protoplasm,  25,  39. 

chemical  composition  of,  28,  50, 
51. 

functions  of,  40. 

properties  of,  28—32. 
Proventriculus,  115. 
Psalterium,  116. 
Ptyalin,  84. 
Pulmonary  artery,  133.  • 

circulation,  142. 

veins,  134. 
Pulp  cavity,  81. 
Pulse,  137. 

absence  in  capillaries  and  veins, 

141. 

Pupil  of  eye,  300. 
Pure  food  laws,  46. 
Pus,  122. 
Pylorus,  88. 
Pyramids  of  kidney,  248. 

Quality  of  sound,  314,  318. 

Rabbits,  organs  of,  *22. 

teeth  of,  110. 
Racemose  glands,  83,  97. 
Radial  artery,  144. 
Radius,  160. 
Rectum,  *76,  96. 
Reflex  action,  265,  278. 
Refuse  of  foods,  42. 
Renal  arteries,  144,  250. 

veins,  250. 
Rennin,  89  n. 
Repair  in  body,  29. 
Reproduction,  of  amceba,  *31. 

of  bacteria,  33. 

of  yeast,  37. 
Reptiles,  brain  of,  *289.  ' 

circulation  of,  157. 

locomotion  of,  207. 

skin  of,  244. 

Resonating  chambers,  315,  317. 
Respiration,  209-231. 

calorimeter,  *55. 
Respiratory  region  of  nose,  297. 
Rest,  necessity  of,  204,  285. 


330 


INDEX 


Reticulum,  *115. 
Retina,  302. 
Ribs,  168. 

movements  of,  174. 

structure  of,  174. 
Ridges  on  skin,  233. 

of  intestine,  94. 
Roasting  meats,  54. 
Rolando,  fissure  of,  275. 
Root  of  tooth,  79. 
Rotated,  181. 
Rumen,  *115. 
Running,  200. 

Sacculus,  311. 

Sacrum,  162. 

Saliva,  82. 

Salivary  glands,  82-84,  *83. 

Saponification,  97. 

Scapula,  169. 

Sclerotic  coat,  300. 

Sebaceous  glands,  238. 

of  eye,  299. 
Second  wind,  222. 
Secretion,  251. 
Semicircular  canals,  311. 
Semilunar  valves,  133. 
Sensations,  of   hunger  and   thirst, 
294. 

of  pain,  293. 

of  sight,  304. 

of  smell,  297. 

of  sound,  314. 

of  taste,  295. 

of  temperature,  293. 

of  touch,  292. 
Senses,  291-314. 

general,  293. 

of  hearing,  308,  314. 

of  sight,  298-307. 

of  smell,  296-298. 

of  taste,  84,  294-296. 

of  touch,  291-293. 
Sensory  cells  and  fibers,  278 

hairs  of  ear,  313. 

hairs  of  nose,  297. 
Serous  membrane,  131. 
Serum,  119,  120. 

hygiene  of,  124. 
Shaft  of  bones,  175. 
Shedding  of  teeth,  79-80  n. 
Sheep,  alimentary  canal  of,  *115. 


Sheep  —  Continued. 

kidney  of,  248. 
Short  bones,  177. 
Shoulder  blades,  169. 
Sight,  sense  of,  280,  298-307 
Sigmoid  flexure,  *76,  96. 
Singing,  319. 

of  birds,  319. 
Sylvius,  fissure  of,  275. 
Skeleton,  159-192 ;  see  Birds,  Frog, 

etc. 

Skin,  232-247. 
Small  intestine,  *76,  92-95. 

absorption  in,  104. 
Smell,  sense  of,  296-298. 
Snakes,  locomotion  of,  208. 

fangs  of,  110. 

ribs  of,  188. 
Sneezing,  225,  280. 
Soap,  97. 

Soft  palate,  77,  84,  *85. 
Solar  plexus,  267. 
Sounds  of  the  heart,  136. 
Soups,  53. 

stock,  178. 
Speech,  317. 
Sphenoid  bone,  170. 
Sphincter  (pyloric),  88. 
Spinal  column,  162-168. 

of  child,  173. 
Spinal  cord,  of  frog,  270-271. 

of  man,  21,  256,  260. 
Spinal  nerves,  of  frog,  270. 

of  man,  260-266. 
Spinous  processes,  365. 
Spleen,  21. 
Splenic  artery,  144. 
Spongy  bones,  171. 

bone  tissue,  175,  296. 
Spores,  34,  38. 
Sprains,  185. 
Standing,  199. 
Stapes  bones,  *309,  311. 
Starch,  digestion  of,  84,  97. 

manufacture  of,  in  plants,  47, 
48  n. 

storage  of,  49. 

test  for,  45. 
Starfish,  *187. 
Sternum,  168. 
Stewing  meats,  54. 
Stimulants,  62. 


INDEX 


331 


Stirrup  bone,  309,  311. 
Stomach,  21,  *87,  88-92. 

absorption  in,  104. 

of  rabbit,  *22. 
Stomata  of  leaves,  48. 
Striped  muscle,  *198. 
Structure  of  animal  bodies,  20-21. 
Sublingual  glands,  83. 
Submaxillary  glands,  83. 
Suffocation,  225. 
Sugar,  digestion  of,  84. 

in  protoplasm,  28. 
Sulphur,  6. 

Superior  vena  cava,  133,  144,  *145. 
Suspensory  ligaments,  302,  *303. 
Sutures,  172. 
Swallowing,  85,  86,  87. 
Sweat  glands,  *237,  238. 
Sweeping,  227. 

Sympathetic    nervous    system,    of 
frog,  269. 

of  man,  201,  266,  268. 
Synovial  membrane  and  fluid,  180. 
Syrinx,  320. 
Systemic  circulation,  142. 

Tactile  corpuscles,  235,  291. 
Tarsal  bones,  162. 
Taste  buds,  *295. 

sense  of,  84,  294-296. 
Tea,  63. 
Tear  bone,  171. 

glands  and  duct,  298,  *299. 
Teeth,  human,  77-81. 

care  of,  107. 

comparative  study,  109-111. 
Temperature  of  blood,  125. 

effect  of  alcohol  on,  243. 

regulation  of,  239. 

sensations  of,  293. 
Temporal  bone,  170. 

convolutions,  280. 
Tendons,  23,  180. 
Terminal  brush,  259. 
Tests,  for  nutrients,  44—46. 

for  carbon  dioxid,  8. 
Thigh  bone,  162. 
Thirst,  sensations  of,  294. 
Thoracic  duct,  *150. 
Throat  cavity,  84-86,  272. 

absorption  in,  104. 
Thyroid  cartilage,  315. 


Tibia,  162. 

Tissue,  23,  28,  39 ;  see  Bone,  Carti- 
lage, Muscle,  etc. 
Tobacco,  64. 
Tongue,  in  man,  81—82. 

in  other  animals,  111. 
Tortoise  or  turtle,  245. 
Touch,  291-293. 
Toxins,  123,  223. 
Trachea,  *85,  *212. 
Transverse  colon,  *76,  96. 
Treatment  of  cuts  and  bruises,  153. 
Triceps  muscle,  195. 
Tricuspid  valve,  132. 
Tuberculosis,  224. 
Tubules  of  kidney,  249. 
Turbinate  bones,  171,  296,  *297. 
Tympanum,  308. 

Ulna,  160. 

Ulnar  artery,  144. 

Urea,  formed  in  body,  18. 

given  off  by  kidneys,  249. 
Ureter,  248,  *249. 
Urethra,  250. 
Urinary  bladder,  250. 
Urine,  249. 
Utriculus,  311. 
Uvula,  81,  84,  *85. 

Vagus  nerve,  of  frog,  269, 

of  man,  279. 
Valves  of  heart,  132-136. 

ileo-coecal,  96. 

in  veins,  *138. 
Vegetables,  cooking  of,  55. 
Veins,  129,  138. 
Vena  cava,  133,  144. 
Venous  blood,  147. 
Ventilation,  226-227. 
Ventral,  21. 

horns  of  gray  matter,  258. 

roots  of  spinal  nerves,  261,  264 
Ventricle,  131. 
Vermiform  appendix,  96. 
Vertebra,  162,  *165. 
Vertebrates,  20. 

classes  of,  20. 

kidneys  of,  252. 

nervous  system  of,  288. 

skeleton  of,  186. 
Villi,  *95. 


332 


INDEX 


Vitreous  humor,  302. 
Vocal  cords,  315-316. 

organs  of  man,  315. 
Voice  and  speech,  315-320. 
Voice  box,  315. 
Voluntary  muscles,  194-201. 
Vomer  bone,  171. 

Walking,  200. 

Wastes  of  body,  18,  29,  210. 

given  off  by  kidneys,  249. 

given  off  by  lungs,  210. 

of  food,  72. 
Water,   amount  in  body,    16. 

composition   and  symbol,   9. 

given  off  by  kidneys,  249. 

given  off  by  lungs,  210. 

in  protoplasm,  28. 


Water  —  Continued. 

test  for,  7,  46. 

uses  of,  52. 

Wax  glands  of  ear,  308. 
White  corpuscles,  26,  122,  126. 

matter  of  cord,  258. 
Windpipe,  85,  *212. 
Wisdom  teeth,  79. 

X-ray  pictures,  159. 

Yeast,  35-39,  *37. 

changes  caused  by,  35. 

reproduction  of,  37. 

uses  of,  38. 
Yellow  spot,  305. 

Zoology,  4. 


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